I'll have to look again, though I've finished a song in IM I overfilled with a score greater than zero
I didn't realize that by "IM", you meant IronMode. I've noticed the few times I tried IM that it does let the song keep running in the background, so theoretically, even with your score reduced to zero, a "gravity match" could still occur from the remaining columns that might have had stuff in them. Does your ship, uncontrolled by you, still pick up blocks after that point?
Even so, this would be an almost useless bug to exploit, as whatever positive score you had at the end of the round would be a pittance compared to even a mediocre run that you actually completed without overfilling.