I'm very sure you can't give your Gate away, with the sole exception of trading it to Truth as part of a hefty deal. And I'm sure that Truth only agreed to that deal because Ed defended his choice in exactly the right way. Nine out of ten people wouldn't have been able to pull off what Ed did. I know I wouldn't be able to. Such selflessness is hard to find.
Plus, I'm sure each person's Gate is only able to be activated by that one, specific person. Ed can only use Ed's Gate. Al can only use Al's Gate. Etc., etc. The only reason Ed was able to get out was because Al was there to subconsciously manipulate his Gate. Even if you could give your Gate to someone else, they would get a Gate they can't use. I bet Truth would laugh at that and chastise them for it in some way. This sort of makes sense since everyone's Gate is personalized. The stylization for Ed's, Al's, Roy's, and Father's were all different. Each one was meant for that one individual and no one else.
“Power in the hands of the reformer is no less potentially corrupting than in the hands of the oppressor.”