It is just another ridiculous exploit that the players have found. It's agony to watch them fake a neck injury whenever they decide they need a penalty. An argument could be made for a crusher tackle in almost every set.
As has been said, the only way to stamp it out (and not punish the poor bloke who will actually get hurt once in a while) is to force them off the field for an assessment. This shouldn't be a free interchange though.
Oh and while we're at it - when are they going to finally clamp down on the Video Ref being involved in gameplay decisions?!?!? A couple of years ago they came out and said that the video ref would only be used for try-scoring situations, then proceeded to ignore their own advice. Then they came out and said it could only be used in a situation where a player would be put on report, and I'm pretty sure they're once again ignoring that. Just leave them out of all decisions unless a (potential) try has been scored.