What I did for Less-rabi was spec one shaman with reverbation, remove his dps key so he did nothing but interrupt, and have this macro on my main, with the stopwatch shown and center screen:

/script Stopwatch_Clear()
/script Stopwatch_Play()

Above 50% he casts every 10 seconds
At 50% he'll cast
Below 50% he'll cast every 5 seconds

Just spamming wind shear on my shammy wasn't good enough, it always went off a split second too soon.
So using the macro above, I just cast when I saw 4.95-5.0 seconds since the last time. Mostly I'd get the interrupt before seeing the cast bar.
Got it on the second attempt with this method, after about 10 failed attempts trying other stuff.

Now I just have Volajz's quick demise left . I can't seem to get below 2.30.