Tough to enforce. I guess you could say no subs except for the "injured" player. You'll have three or four guys cramping just to get the third down package on the field. Now you have four guys to make sure sit a series. Do we give them water? It's not really the point. You don't have to have a huddle to set up the defense, that doesn't solve anything. And is totally worth it to rest, water, and reset a struggling defense.
I think it's something that has to be addressed but you start, as I said earlier, with baby steps. And then adapt from there. Huddling definitely allows for coaching to occur. There is no magic solution to this. It's a shame that it is being abused as much as it is. But, "them is the breaks".