I think they can be the second highest conference champion.
They would need to win all of their regular season games and the conference championship game.
There is only one SEC team above Byu in the rankings (Texas.)
Tennessee is ranked right below Byu. If they lose another game before the conference championship game, even if Texas goes undefeated until the conference championship game, Byu has a chance to move up if Texas loses the conference championship game. If Tennessee wins out, I think they would jump Byu, but I don’t think they would jump Byu if they lose one more game in the regular season.
The above scenario would mean that the eventual SEC champion would have at least two losses Before the conference championship game and would be going into the conference championship game likely ranked below Byu. In this scenario, Texas would also then end up with two losses and would not be seeded based on conference championship ranking.
It would be amazing to make the playoffs in any scenario, but to make the playoffs as a number two seed would be crazy. I think this is unlikely but possible given the above.