There are a few points you can make here that help make BYU's case.

For all of the sports that play on Sundays, the main adjustment would need to be a change in the tournaments. All other schools could continue to schedule matches with each other on Sundays, only the regular season games with BYU would need to exclude Sundays, which wouldn't be much of a change. It gets a little more complicated with things like track meets, swim meets, and golf tournaments. Golf is easy because BYU could simply do a separate round at a different time like we did with the most recent NCAA tournament for women.

A listing of the Trammel's article around the challenges involving BYU's Sunday play policy is really good, some of those points should be included. It'd be really nice if someone went all BamaCoug on the schedule to put together different options on how it could work with BYU in the Big 12.