Depending on your spec, end your macro with:


Blood:
/cast Rune Strike

Frost:
/cast Frost Strike

Unholy:
/cast Death Coil

Preface this with four to six abilities, which combine for two Blood, two Frost and two Unholy runes.
The castsequence should run pretty good.



Alternatively, put abilities on different buttons and mash all of the buttons.
If something cannot fire, it won't even if it is pushed.

You can "weigh" an ability, by including it three times on seven buttons.
Or whatever you want to do.