Unlikely but not impossible.

Since the Rose bowl is hosting the playoff, they will displace the PAC-12 champ if they are not in the top 4. Right now, I don't see any PAC team that will be rated that high.
The Pac-12 champ will very likely be placed in the Fiesta Bowl due to geography which plays a part in committee placement.
On the other side, should the MW champ get the G5 auto-bid, they would most likely be assigned to the Fiesta Bowl due to geography of the conference. The bowl would have no say in committee selections and the committee besides looking at matchups takes geography into account so there is less travel for the teams and fans.

It would setup a scenario that wouldn't happen in any other way and would really upset the PAC I'm sure.