Personally, I am pretty direct and perhaps the below will offend you and others here but either way I think that the bull needs to be grabbed by the horns here:-
I can, to a certain extent, sympathise with your motivation but I think that it will do a disservice to those that genuinely have ADHD if you game the system like this.
I was sorely tempted to do something similar for my DD when I discovered that she has zero backing from the govt because she has the IQ and achievement but no LD and having an LD on her 'chart' would have been the 'open sesame' for her.
In the end, I decided that ethically it isn't something that we can do and not feel dirty inside as it would mean resources that are already stretched would be stretched further by our 'faking it'.
Like others have said here, I would try to find out what the real issue is. Is it merely an intrinsic motivation issue, an audio processing issue ( I know all about those ) or something else?
Maybe it is 'boring' for your kid at school but the sooner your kid learns that he is measured in life by achievements ( things have BEEN done) instead what potentially may have been achieved the better, IMO.
YMMV
