The system already does the random roll for you, and it asigns the drop to your loot list.
if you do not want the piece, you can simply trade it from the loot list to another player.

adding more player intervention methods to the game opens up alot of abuse. especialy if you get a master looter type setting involved(as nice as it is, you will get more abuse of it with people ninjaing stuff then in any other system out there)

With this in mind, dont run things with people at random if you care that much about drops. Run it with people you trust who know how to use the trade button in the loot window.