If a person has an IED on them, they're probably going to just use it. There's no logical reason to scare everyone off with a rifle before you set it off. That coupled with the 2% of shootings they've seen them used(which is probably only once or twice ever) and the fact that they can rig them so that releasing a button results in detonation, I'd say just don't clutter your mind with IED equipped shooter defensive "training".
If a guy is shooting people, the gun is overwhelming likely to be his best attack weapon.