Idea Wagering system

Recently i had some really fun raid/team fights, which were really fun. Since there is hardly pvp action at spawn i thought about ways how to increase pvp action at spawn.

Here is my idea:
You can create a team with as many members as you want and /wager a different team. If the team accepts each team has to pay a startig fee of 15 gold per player. You can have those fights at spawn or somewhere else at the map if you dont want to get jumped by any other Players. While you are fighting you can NOT warp, as long as not all Players of the opponents team are dead, so that it doesnt make sense to kite.
Once all players of one team are dead each Player gets 30 gold (hes and his oponents) back and a wager key. With this wager key you can open chests like the koth chests.
Rewards could be :
64 obby
16 iron blocks
32 Diamonds
Enchanted books
32 gold
beacons
.....

while you are fighing other players can jump as i dont want the fights to happen in closed Areas a this would take away the hardcore aspect. However jumping is quite useless as it would make more sense to join the wager team as you have a chance to get a key then.

I just dont have any ideas how to prevent farming wager keys by making stonesword 1 v 1s or 2 v 2s or what so ever. THe only way i can think of is to make a entering Price of 20 gold which you dont get back.


Any ideas od thoughts?