There is no tank swapping in any 24 man raids, so a raid wide Shirk isn't necessary.

If you do have a tank spamming provoke, just drop tank stance and let them tank. Don't try and fight it, just let it happen.

Although, I rarely run into situations in 24 man raids where that issue even comes up, so maybe it is more of a region thing, however, this also goes back to the start of this topic. The tanks just need educating. No matter how you try and 'fix' things, someone will find a way to do something stupid.