This isn't the first time I've been in a league where the commish had to PM everyone asking them not to claim a player. I commish fantasy baseball leagues and if this situation came up there, I have the ability to put that player back on the original roster and if need be, lock any team from making roster moves.
I know this is not currently an option in MFN, but why not? As MFN gets more and more user created leagues, administrators need this option.