I only did this once, about a year ago. When I executed the pilot in flight and took over, I got the experience. But maybe they changed it since then..
That doesn't seem very abusable to me, considering the new pilot needs to have been in the cockpit for the duration of the trip, and you can't force a pilot change unless you're able to kill the other. So for this to voluntarily occur, one guy is just forfeiting his XP.
That is, provided the first pilot doesn't accidentally abort the travel by leaving the cockpit in the first place.