I'm of the opinion that if it feels ok, do it. I've never had a problem doing them front or back, but by the same token, dips annoy my shoulders to no end. That being said, be honest about it. You've got bad shoulders to start with, and a run away btn press is tricky thing to deal with.
Find a full power rack, and do them off the pins, also humble yourself, and do them standing. It's much easier to dump them standing if you get into trouble. If you're self conscious about it, buy a pair of #44/45 or #55 bumpers, and practice in your basement. Generally you can add similar amount of smaller iron plates in weight to a side, as long as you've got a good full sized heavy bumper as the first plate. It's not too rough on the bar.