It is interesting that they started him on Risperdal instead of a stimulant med. Risperdal is a great med for bipolar - especially dysphoric manias and/or mixed states instead of euphoric manias. So I am guessing that early on they might have been having trouble figuring out if he had Bipolar or ADHD?
At any rate, that is a tough combination for a child to have - and perhaps even harder on the parent.
The problem is that both areas need to be treated. While the Risperdal can be very helpful for the biopolar - I am pretty sure that it is not going to help the concentration problems of ADHD. Essentially, " Controlled studies have shown that children with Oppositional Defiant Disorder and other disruptive behavior disorders show short and long-term improvement when taking Risperdal. There may be a place for the atypical antipsychotics in some individuals with AD/HD and agitation. The atypical antipsychotics can often cause weight gain in both children and adults. Abilify, (aripiprazole) is less likely to cause weight gain or metabolic problems." (from - http://www.baltimorepsych.com/NonStimulants.htm).
Point being is that if all he is taking now is risperdal and he is not getting a help either med wise or behavioral therapy for his ADHD - then his ADHD is probably making both his and your life pretty miserable.
This is a really good site for dealing with co-morbid disorders. The end of it has some very helpful suggestions. Its worth your time to check it outl The site is - http://www.pediatricneurology.com/full.htm
All in all, I get the feeling that you have been dealing with the bipolar issues (completely understand that), but may have neglected the ADHD part. If you would like more help with that please post over on the ADHD forum (where I am also the CL.) found here -
http://www.medhelp.org/forums/ADD---ADHD/show/175
Best wishes!