This is exactly what I'd do.
I will not trust Doc Rivers to do the job. Instead, if I were DA, I'd have one of the assistant coaches carry a stopwatch and click on/off for every time Pierce gets on the court.
When the clock strikes 24 mins, Pierce is automatically benched. During the regular season, no exceptions are made, period

! Yes, a few games will be lost in the process, however, Doc needs to learn how to manage his rotations.
Then, Doc will realize that he'll need to really cut down Pierce's first two quarter mins so that he can contribute at least half to 3/4s of either the third or the fourth quarter.