Follow-up: It helped flying in and out of smaller airports. Arrived early. Asked at the American Airlines counter about checking the bag for free and it wasn't a problem. At the counter, they said Tim could even have an extra carry on so long as it was medical stuff. It took a long time to make it through security. Every can was checked for explosives and every surface and item in the carry on was carefully checked. His pat-down on the way back should have been preceded with dinner and a movie ;-). But all the TSA were polite and professional. Tim had a note from a doctor, the blue card you can print from the TSA site stating that his jaw is metal and he's on a feeding tube.

Thanks to everyone for the advice!