I don't know of specific technology - but I had a student with CP a couple of years ago, and he did all his class work and homework on a computer (sometimes a lap top, sometimes a school desk top, sometimes his DynaVox - he was also unable to speak clearly because of the CP), and then emailed it to the appropriate teacher, all through middle school. He numbered the problems to match the worksheet and typed all his answers in that way. Why do his answers have to be on the worksheet? Can't he just type the answers, print them, and staple them to the worksheet? Or email them?
For work done at school - the school should have computers, and possibly something like an AlphaSmart (portable keyboard) that he can use. If he's in special ed, talk to his special ed teacher and get assistive technology added to his IEP; if he has a 504 plan, get the use of assistive technology added to his 504 plan. Speaking as a special education teacher, there's no reason why he should have to do the work ON the worksheet, as long as he is demonstrating his understanding of the material - and if he has physical difficulty holding a pencil, keyboarding for his school work is a life skill he needs to start working on as soon as possible
