It's not worth the headache it causes.
No reason to screw BYU over now and get criticized all season for it. Just put them high enough that people don't care anymore, then just drop them a couple of spots in the final poll. It worked well with TCU when they got a big win the last week of the season and dropped from #4 to #7 in the final poll. Honestly, most people got pissed for a few weeks and then Ohio State won the Natty as the #4 anyway...
Now only BYU and TCU fans remember that it even happened.