You might also want to do a little more than have the pilot just 'trim it out at say 6-7000 feet heading out to sea' because - well I must admit here that I've flown gliders far more than light aircraft - but nothing I've flown ever keeps its wings level for long if you don't make at least the occasional small correction, so the aircraft would probably end up going round in circles, and crash not all that far from where the pilot jumped! Better that he hire an aircraft with an auto-pilot, and set that to head the aircraft out to sea - that will guarantee that it keeps going in a straight line till it runs out of fuel. It would also adjust for centre-of-gravity changes that will occur when the pilots weight leaves the aircraft.
Maybe a few light aircraft pilots out there could do a quick test - or even already know - how long does your aircraft keep flying straight-and-level for if you take your hands and feet off the controls?