And one month later, I DID. 
I think we should use battle tents as mob arenas. Custom made arenas, maybe? The actual arenas would be somewhere far away from the tents because the arenas would probably go into Rusturf Tunnel and Desert Underpass if it was right under it.
By 'battle tents', I assume we are talking about the Battle Frontier. In which case, a plugin that could do this well is Mob Arena. It basically allows custom arenas to spawn mobs in rounds, and also allows for rewards every round, if you want. It's also very customisable.
Also, I think that, if you pass them, you could bet like, maybe 5 sponges, or whatever. These are like Battle Frontier Coins, and can be used to purchase awesome things that normally wouldn't be obtainable elsewhere.
How to accomplish this? Well, with MCEdit, there's a filter that is made by Antvenom I think, and allows for chests with the right inventory placement to be turned into villagers with trading such as that. Personally, I think the sponges and villagers could give a realistic feel to it. And it would encourage people to actually go in there and battle.
