How long are the parts? Do they need a pitch reference? If short/no was your answer, you can toss a pair of headphones on the ground, crank the shit out of them so they can hear the click/lead in, and then drop the volume before they all do the part. I do this when tracking vocals sometimes as a way to let the vocalist be in the same room and not have to be wearing headphones; he wears headphones, I manually duck the volume around his takes. Bleed goes away and my ears don't get sore and sweaty.