I hope this works for you :].Ok, you may have a little re-course in this. Let me get this straight. He let you into the dealership's work area, left you alone to do work on a car (which is technically his) and you got hurt in there.
You can majorly screw them b/c that is a huge NO NO for the dealerships insurance. From my understanding, customers getting hurt in the work areas will drive up the dealerships premium. You need to keep a very good paper trail from now on. Your hospital details, who you spoke to at the dealership, who let you in there to do work on your own, time and dates. I'd bet that if you threatened them with a lawsuit they would give you back your car and just cancel the deal.
I hate seeing nice people get screwed .. you better be a nice person! Lol.