I had this problem with my current grow in my signature. Well, almost. Removed quite a bit about a week after moving to flower but was a bit conservative because I had no idea how much their random genetics would stretch.
Wasn't a bad thing because quite a few more tops made it to the canopy while I kept it roughly the same height with supercropping. Still wound up taking a ton more lower crap off just last light cycle at 28 days in. At least that's the last of that. I just wish I would have got it done a week sooner. They don't seem to be noticing too much though.
The best way to get no popcorn is with scrogging, just saying. At least scrogging has always seemed easier than tying down a whole bunch of different branches in 2-3 different places and having to adjust them all every few days during the stretch.