On the Shattered Worlds server, you can use the /bank command to do credit transfers. When I asked one of the players over there how they prevent credit stacking, he told me that you couldn't use the /bank deposit command until your character had been on the server for an hour.
Now, I know they use FLAC over there, so it might not be possible to implement with FLHook, but if it could, I'd love to see it implemented the same way here.