Could it perhaps be made so that entering a Danger Room (http://wiki.spiralknights.com/Danger_room) is a group decision? In my experience, unfortunately, people will not ask if you want to go in one, and will just open it. Perhaps those who choose "no" could simply be removed from the party.
99% of the time, I personally don't want to go in one and 99% of the time, nobody will ask. That's only going by my personal experience, I'm not trying to say every single player does this. Obviously, I'm very unlucky!
Thanks for your time! :)
A good idea would be adding a vote system, but since the masx players number for the dungeon is 4, tie is a possibility.