Wannabe, I am so sorry your ds is having to go through this. We have been there with ds1 and you feel so helpless, but there are things you can do.
If you don't want to move him to another school, you are going to have to come down hard on the school to make sure they take it seriously and deal with it appropriately. Bullying is bullying, be it verbal, physical or social exclusion and shouldn't be tolerated in any school.
My ds is now 9, nearly 10 and has AS and at your ds's age was really struggling.
First of all you need to be keeping a record of all the 'incidents' and comments that your ds tells you about and then you need to arrange to see his teacher. I would ask in writing for a meeting stating what its about in the letter. This will start your paper trail for getting it dealt with properly by the school.
You could also ask for a copy of the school's anti-bullying policy, as this will give you a good basis to demand action and I also found it useful to quote from the sections about bullying from Tony Attwood's book, pointing out how easy it is for children with AS to be targetted by bullies.
If there is no joy from the teacher, you have to take it up a level. So either head of year, head or head of school - depending on the structure of your ds's school.
In each case, confirm in writing what was said at the meeting and what action has been agreed, including a date when its success/failure will be assessed.
Also, have Autism Outreach (or the ASD/CLD Inclusion Team as they are called around here) been brought in to support your ds and his teachers? This should have been done as soon as AS was suspected or at the latest once he got his dx, as there's a lot they can do to help. First of all they can do some staff training on ASD awareness, which will help teachers to understand and spot the signs of subtle bullying and/or social manipulation. Secondly they can arrange some peer awareness training, which usually takes the form of a general session around differences and tolerance, rather than discussing particular children and their needs. This brings the whole SNs topic out into the open, to be openly discussed by all the children and ensure that they are all aware of appropriate behaviour, inclusion and tolerance.
If the outreach people can't do this for a while, you can request that it is covered by the school under the remit of Social and Emotional Aspects of Learning, which is a compulsory element of the curriculum. It should have been covered already by this point and if it has, the children involved have absolutely no excuse, because they will already be aware of appropriate behaviour and inclusion.
Another idea is for the school to build a 'circle of friends' around your ds, where they select a number of appropriate children and work with them to develop a sort of mini-support group of friends who will look out for your ds. Again the outreach/inclusion team should be able to help with this. You can google for examples of how this has worked in other schools.
We have pushed for all the above things to happen and ds is now much happier at school. He still only has a couple of true 'friends', but the other children are far more inclusive than they were and more tolerant of his quirks.
Most importantly, we really pushed for the bullying to be dealt with, in my ds's case it was physical as well and pretty awful at times, but the emotional bullying was just as hard for him to cope with. With all our written and diaried evidence of bullying, the school had no choice but to tackle it swiftly and come down hard on the bullies. Their parents were brought in and they were given specific consequences for any bullying behaviour. The school also admitted their anti-bullying policy wasn't worth the paper it was written on and scheduled it for an immediate overhaul.
Another thing our school did was to mix up the classes before they went into this academic year. They moved his worst bullies and tormenters into the other class, but made it look like they were just mixing up the classes in general. They do this occasionally anyway in the upper juniors with classes that have been together a long time to prepare the pupils for being mixed up in secondary school, so it wasn't an issue. I think this, more than anything probably helped the most, because he no longer has to share a classroom with them so doesn't have the constant low-level bullying, snide remarks, accidentally being bumped into or having his stuff knocked off the table etc to deal with and the bullies now mix with boys from the other class at playtime rather than with ds's class.
With regard to birthdays, I always keep them small and dictate a definite number of friends allowed. In ds's case he is allowed, three friends maximum plus his brother and cousin. This means that I can easily chase the parents to make sure they're all attending and also we get to do more fun things because it costs less. Shame on the other childrens' parents for letting that happen to your ds, it makes me so angry when parents don't model appropriate behaviour to their children. They are effectively allowing them to grow up into bigotted predjudiced bullies. 
He hasn't been invited to any of the other boys' parties - other than his best friend's - since early infants when they stopped doing whole-class invites. We try to balance this by making sure he has his friend round to ours maybe once or twice a term and making his favourite tea etc.
Sorry for the humungous post. I just know what it feels like to be in your shoes and wanted to get all my ideas for improving things down while I have the chance.