I live in Missouri, in high school I had my banshee street legal with car license plates on it. The way I did it was just take it to some hole in the wall mechanic that does car inspections. The guy who did ours didn't even take them off the trailer, he just looked at the serial #'s and wrote up the inspections. We took them to the DMV and the lady was pissed, asking questions about it having seat belts, turn signals, blah blah blah, and we just referred her to our inspection slips. She even pulled out a book that was probably 50 lbs and started trying to find a way not to give us the plates.
Every cop I ever saw pulled me over though. They would tell us there was a loop hole in the law and it would soon be fixed, never heard anything after that. They'd ask why we didn't have helmets on, and legally we didn't need them because it was a 4 wheel vehicle. Never got a ticket or anything, one even told us that we had to have a big orange flag on the back of it which is BS.
Point is, at least in MO, if you have the inspection slip there isn't much they can do.