Originally Posted by dhc8fo
Do either of these guys still have a current CFI rating? If so, the medical shouldn't be an issue for a high altitude endorsement. I am too lazy to look it up to be 100% sure, but I am pretty sure this is the case. Many types of instructing for advanced ratings/add-ons don't have the same medical requirement. Worth a look.
You need a PIC for the airplane. I would assume the PIC would also have to be the instructor for the endorsement.