Problem here is that if we give players a chance to veto/boycott some elements, the whole auction is pointless.
I personally think it's a shame that some people hate a specific element so much, they refuse to play it. A true PvP player would take this as a challenge and prove that it's not about the element, it's about the player.
I like Icybrakers suggestion of picking preferred elements, and if the preferred element matches with the bidder, a small bonus gets added to bidding prize. However this system would give advantage to popular elements because they wouldn't have to spend so many cards for buying players. Advantage = a bad thing.
I'm inclined to go with a system where everyone chooses 3 preferred elements without any bonuses. They would serve only as a way for Masters to see if that specific players really wants to join a team. You could "force" a player to join your team but then again might be better to pick someone who wants to join your team.