You might be able to put a disc syestem from a 5th scale or mod a disc set up from a 8th.
I think it wont be worth the trouble or money but that is why we are all different. Good luck. Mark.
Jatoman,
Your best bet would be to buy a wreck 8th scale to rip the disk brake cam,pads,backing plate and linkages off it. Any brand any condition it will be the cheapest way. Sorry dont know where you look for that as im from Australia, Try E bay. Mark..