A strong rubber band on the trigger is all it takes on an AR. I have the ready made SlideFire pizza on an AK and it works pretty slick as well. It is all technique. With sufficient technique, it can actually be done with no modifications to the firearm.

However, from practical point of view, if someone was firing at me, I would rather they were bump-firing rather than single shot timed deliberate fire. The safest place is most likely POA.