This is so rediculous. Okay, for all of you who just WON'T drop this stupid idea that you have to comply with 922R, just get a friend to install your parts at his place and then bring you your M4 back. Perfectly legal on your part as you didn't install them. The law says NOTHING about possession, only installation. Then just don't rat your friend out for committing such a heinous crime against god and country.
Problem Solved.
But no, it's not. Because you just want to whine about SOMETHING, and the M4 is perfect, and so the only thing that can be whined about are laws that mention it, so you will then find something else to whine about. Like the fact that you cannot get the Benelli cleaning-kit for it in the States. Stop messing with perfection.