Before the haunt, can players agree to automatically crack the Vault?
You don't have to do anything on your turn, so if all players agree there's no reason you couldn't give the player who discovers the vault all the turns until they open it.

However, I'd suggest this is tactically a bad idea for the players not in the vault. Until the haunt starts you don't know who is on your team. An individual player could increase his or her own chance of winning by grabbing the sweet, sweet loot for themselves. It would make more sense for all the players who stood a chance of opening the vault to rush there as soon as it is discovered, personally I think that would be much more fun.