that the drivers could walk to to the stadium from after dropping kids off. There's also some big open parking lots just east of the stadium I bet they could park the buses in (may have to pay a few bucks).

There's also two different large church parking lots nearby. One is literally across the street and barely north of the stadium. There's 3 buildings that share the parking lot so it's huge. I'm sure that's your best bet. There's another church just east of the stadium a few blocks (still up on the hill). You should maybe have someone from byu contact the building people there to see if you could park there.