Martha,
You may want to contact Debbie Miles-Williams, the University of Leicester archaeology outreach officer, regarding accommodating disabled participants in Operation Nightingale.
"Operation Nightingale is a new Ministry of Defence run project which aims at using archaeology as a means of rehabilitating injured military personnel. It has been founded by Sgt. Diarmaid Walshe of the 1st Battalion the Rifles in Chepstow and Richard Osgood, the Senior Historic Advisor at UK Ministry of Defence. Several of the soldiers have signed up to study for archaeology degrees at the University of Leicester by Distance Learning. At a time when archaeology can struggle to justify its existence to those with little interest, Operation Nightingale is leading the way for other community-based projects to demonstrate how important archaeology is to our future."
http://www2.le.ac.uk/departments/archaeology/outreach-1 for more information (including Debbie's contact details).
Alasdair Brooks