In this current state of college FB, if the back up isn't playing, he transfers. We have two of those on the Husker D in Joseph and Johnson. Neither played much for their teams but people were ga ga that they were highly rated.
The point is, you are not likely to have quality backups and as far as getting them ready, Nebraska has been well known for multiple non starters getting lots of reps. That is why they have so many practice fields in the new remodel.
You are playing with fire on getting game experience. Let's say you get 80 snaps on O or D in a game. How many of those 80 are you willing to put in a back up only to fumble, drop a pass, miss a tackle or blow a coverage? How many snaps are you going to give a vacuum QB just to say you did?