Cross-Realm PVP whisper/ignore

Seems to be a frequent thing right now - LA folks are pissed off to be doing cross-realm, or maybe it's a combo of cross-realm and mercenary? In the past couple weeks, I've had several of them harass me via whisper, and I'm sure I'm not the only one... just basic bashing of playing and donor bashing.

I have asked politely for them to be quiet and play, and they continue to /w. Unfortunately, you cannot ignore them - I assume because it's cross-realm. Can this be fixed? It's fine if we can ignore them, but what other recourse is there when that's not an option?