Fewer calories. The number of calories you need when you cannot exercise is surprisingly small. If you are gaining weight or not losing, you are getting more calories than need. Tricks to getting to healthy weight include avoiding drinking calories (unless of course you are unable to eat solid food safely), avoiding snacking between meals, eating high fiber diet (fiber bulks up in the stomach and reduces appetite.
Depends on injury. Anything that uses energy (calories) will help one lose weight, as long as he doesn't eat or drink back more calories right after the activity. Paraplegics can exercise, quadriplegics cannot. Examples: if rolling in a wheel chair, take a longer route; park a block from school and roll there with the kids; at home, skip dessert and go roll around the block instead. Join wheelchair sports and races.