I managed to express 70ml of colostrum before birth, and then my baby latched on, didn't have a sugar drop and didn't need it. 70ml would have gone an awful long way.
Don't start too early (as it can induce labour apparently) but do start as soon as you can. I can't remember the week you can start from but it's googleable. Don't worry if you only get drops to begin with - I got 0.2ml per breast initially and 2.5ml per breast after 10 days - I expressed 3 times a day and got more out after a hot shower. I needed small syringes to collect into, squeezing a drop onto the nipple then sucking it up with the syringe. It was painstaking. Getting hold of sterile syringes was difficult.
http://www.nhsayrshireandarran.com/view_item.aspx? item_id=4412 is a useful link.
But, if your hospital isn't on board with it you are going to have be jolly bloody minded about using the colostrum.
Some women do what is called 'colostrum harvesting' prior to birth. You can get medicine syringes and hand express into a sterilised bowl then use the syringe to suck up the colostrum (or if you have a OH who would be willing they could hoover up the colostrum drops as you express). You would then freeze the colostrum in the syringe.
A mother here shares her account of colostrum harvesting and diabetes.
From a quick google (always reliable) seems to be quite common to do so if you have diabetes of any kind so I'm not sure why your cons. pooh-poohed the idea that you might as well (unless you have had breast surgery or have another condition that would mean you might have problems lactating that you haven't mentioned).