re: How can the NCAA combat the flopping/fake injuries?

The only "fair" method I can think of is that you give the offense a choice here:

Do you want to substitute for the "next" play? If no, then the defense cannot sub for anyone except for the player who was injured. If yes, then both teams substitute freely.

I'd like to say that the substitute must be the same position as the one coming out, but that's impossible to regulate.