(Search in the Scripts Sections for the past 120 days resulted in no hits.)
I'm sure someone's at least thought of the need for this.
For whatever reason, you as player/pilot leave the cockpit (okay, only a small hand full of aircraft I know of allow you to "get out" and still remain aboard the aircraft: the DC-3 with working toilet ;D , a C130...), you'll want to the aircraft to continue on course.
I see two options for the pilot:
1) Just "get out" and the AI copilot continues on the heading the a/c was on when the pilot left the seat
2) Some sort of autopilot system, with which you would set course, altitude, whatever, before you leave the seat. Some sort of dialog(s).
I know we get into that area of modelling where there can be only one pilot, gunner, etc. But how about:
1) Put the AI copilot in his assigned seat, the player sees it's there.
2) The player engages our copilot/autopilot system, and a "dummy" model is moved into where the AI was; the real AI is moved into the pilot's seat, but invisible to the player
3) Or just move the AI into the pilot's seat.