These are good suggestions. Here's the problem - the fake injury has already accomplished what it was supposed to do - slow the momentum of the other team. Teams have plenty of guys they can sub in after the fake injury, or send someone in for the purpose of faking an injury. So, simply keeping a guy out for the rest of the series isn't much of a penalty.
More severe in game penalties for injury just penalizes the guys that are actually hurt. A cramp, for example. Or having the wind knock out of you. Theses are legitimate reasons for a player to go down, but could also recover quickly.
Penalizing a team AFTER the game will probably be toothless.
In this world, it's hard to legislate integrity.