Two options:
1
I'm flying a bomber / driving a vehicle / captaining a PT boat-destroyer. I want to gun instead of drive.
I type in: .switch pilot
A message window appears to my gunner. "Fork wishes to switch positions. Do you accept? Yes / No"
When he/she clicks "yes", I'm now in their position.
2
If I disco for any reason, or by choice, a message appears...
"Fork has disconnected, do you wish to take-over the mission? Yes / No"
That way flights aren't lost, missions busted because someone disco's.