The only problem is any single player can only have a single boundry, and the player has to stay inside the boundry not outside.
IF you could go outside a boundry then the above plan would work, however that is not the case, and boundries as far as I know can only be square... Now, I know there is a math function someone made once to do area co-ordinates that are not square as an "IsPlayerInArea" function... I dont know if this could be used / manipulated into different geometric boundries.
If so, then it could work.
Searching sa-mp.com...