Why not just a regular vote kick, but don't let the party see how many votes are piling up? If I vote to kick PlayerX, he will see 1 vote against him (not from whom), and nobody else has to know. That way, you don't get a crowd mentality prompting other players to also vote against him. If PlayerX is AFK or a troll or whatever then everyone can independently vote. Since you can't send tells in the instance any ganging up has to be stated in the open for the whole group to see.