Many recumbent-oriented shops also deal with adaptations for various issues. The one in Portland, Oregon (Coventry Cycle Works) sure does. If you want to see what's possible, check out the Lightfoot Cycles site:
http://lightfootcycles.com/
FWIW: there's a local rider who I *think* has Cerebral Palsy that I see on a Sun recumbent trike:
http://www.sunbicycles.com/product_d...&cl1=RECUMBENT . I haven't talked to him- I'm usually going the opposite way.