If you really want something just ask the other player.
Yesterday I did Bryaflox's Longstop Story mode for my atma book and I was hoping to get some gear to my pugilist while doing it.
But when I joined the tank said he'd been farming this dungeon a couple of times now for the infantry set.
So we agreed that if the skirt dropped I would get it, and he would get the other pieces cause that was the one I wanted the most.

It was that simple, now none of us got what we wanted but it was a nice deal and both were happy about it