OP has a Thai ID which means he's registered on a tabien baan and therefore as likely as any other Thai male to be selected for the lottery.

Question: why not enter on his British passport, do visa runs or extend his stay as any other visitor might - but simply use his ID for anything he does (work/school/living). So long as he doesn't need to go to the Amphoe he's registered at, why would there be a problem? They wouldn't even know he's there.

Is he violating the terms of his visa by, say, working? Yes, technically he is. Not trying to suggest OP should do anything illegal but is he breaking any law as a Thai by RIGHTFULLY flashing his Thai ID at an employer or the police ... without the need to even mention a British passport?

One could argue that if he wanted to go this route, he should be as obliged as anyone else to take his chances with the lottery. But then, he's already stated he wouldn't mind doing it if he had to.

I doubt he's alone either. There must be thousands like him around the world.

I think everyone including the op is making a big deal out of this, I know plenty of thais who have done military service not one has anything bad to say about it. Ok so they say sometimes the running in the heat is a little hardwork but its unlikely for the first two years they will have to go to any kind of war because they require training first. It's unlikely he will be sent to prison if he didn't go he just has to explain his situation.

Most people I know who have done the service are incredibly proud of having done it plus you get the added advantage of getting fit and healthy in the process plus you will get admiration and respect of all thai people on top of a salary.

I don't think the government will have a big problem if you don't do it but maybe you will like it too 100 per cent of people I have spoken too loved it

Just go to the Trebbian baan office or embassy and speak with them also with people who did it already

It serves thai people as a whole you might enjoy it drum cool