If there's a known company pilot on board then you'd obviously get them up front, but otherwise, to avoid complete panic down the back, I'd just get on with getting the thing on the ground. Anyone worth their salt could single-pilot an airliner under those circumstances. If it were an incap Captain, and there was a rated and current company captain on board, I would be happy for them to assume the role as Captain, what you have to remember is, is that an FO is the 2nd in command of an aircraft and the choice lies with them as to how they conduct the remainder of the flight with an incap Captain . . . although they'd be wise to adhere to company SOP's and not get carried away with their new found responsibility!
You could use a cabin crew to read out checklists etc, but to be honest, you'd get it done quicker by yourself . . .