That has actually been done numerous times, and has already been discussed in this threadi have a vision...
take the headrest off.. get a piece of wood big enough so you can drill two holes that the posts for the headrest can go thru.. make sure theres a little piece sticking out the front and put a screw through the wood, but make sure the screw has the right thread size so it doesnt strips out the threads on your camera.. put the headrest back on w the posts through the holes and screw on your camera....
im a genious