NFHS 9-1 simply states, " An offensive player shall not push, pull or lift the runner to assist his forward progress". Sometimes simple common sense can successfully supersede rigid, or excessive "interpretation" of written instructions.
Forward Progress (NFHS 2-15-1) is defined as, "end of advancement of the ball, toward the opponent's goal, in a runner's possession....".
There is no NFHS definition for, or of, "a pile", so it seems reasonable to accept the judgment of a competent calling game official whether Forward Progress, of a runner, was continuing on it's own volition, or had ended at which point it may have been Illegally assisted by another offensive player (or players in a "pile").
When Forward Progress has ended, NFHS 9-1, does not appear to apply to a dead ball situation, and a "protective officiating " tool of reminding players to "Don't do that" (or something similar) seems a practical instruction to avoid potential danger and unnecessary penalty in light of the fact any unearned advantage/disadvantage has been eliminated by promptly establishing the end of forward progress.
Should similar behavior persist, or be unusually flagrant after forward progress ending has been indicated, alternate remedies are available.