Well I think the proper way would probably be lower them down along side your body. Like sliding your elbows down your sides and letting your shoulders rotate. At least this way if it tumbles a bit it's usually heading along the bench and is probably a clear area. This works best for incline I suppose.
The way lots of guys try to do it is to lock their elbows at their side and just kind of try to toss it out sideways. This way the weight can tumble out sideways which is often right into the guy on the next bench.
If you're really worried about shoulder injury and don't want to have to throw them down then having someone hand them off to you would work best.
If all else fails just make sure ppl are out of your way if you have to drop them.