Not sure it's possible as the FCS season ends the week prior to the conference championship games and the playoffs start the following week. Only way that we could have scheduled a FCS team was to play them this week during the bye, and getting guys healthy is much more important.
If they really want to play the game, they aren't limited to just UTSA. They could call up UMass, Florida, FIU, Georgia Tech, UCF, Memphis, Arkansas State, and Miami. UCF, Memphis, and Miami look like they'll be busy that week while FIU is still in the mix to play in their conference championship. However, at this late of a date, not sure that it would be feasible logistically.