The Couch Potato Telescope (a chair-based binocular mount) would be easy to adapt to a wheelchair.
Sim sells the completed chair, a kit of parts, or just the plans and parts list. These are very easy and comfortable to use.
More information is here.
They look like this:
and you could buy only the parts for the upper supports (without the plywood base and/or chair parts) and adapt it very easily to your chair using simple handtools.
The universe is not only stranger than we imagine, it's stranger than we CAN imagine. --- JBS Haldane
Come visit me at Comanche Springs Astronomy Campus (we're on Google Maps) in Texas.