Don't ask him to lie. Ask for the time off (even if it is likely to be refused) and then take it anyway. Very unlikely that you will be fined if he has good attendance and it's only a couple of days. Is he under 5? If so, he's not legally obliged to be in school anyway.
PP is incorrect by the way - schools do not generally let you have 10 days off - it's entirely down to the individual school. Sounds like yours has a "no leave at all in term time" policy.
Honestly your DS will drop you in it when he returns to school as they always do. Check the school website for the attendance policy and remember legal requirements for fining parents who take children out of school cannot be enforced until the term after your child has turned five.
I would speak to the head and if your child has a good attendance percentage then generally they do allow you to have up to 10 days off at some schools.
This is rarely allowed at my DS's school! I am planning on taking him out for 2 days to attend a family party which I will have to travel to (5 hours there and back). My DS is in reception. I haven't asked for the time off as I know from others they don't allow time off for this. I'm just wondering about ringing in and pretending he is unwell. Has anyone done this? I have concerns about his teacher then asking my DS if he 'feels better' when we come back and him then acting confused! I'm not sure about asking him to lie.