hmm.. tried a few variations around this...

Code:
/stopmaco [channeling]
/castsequence Arcane Blast,Arcane Blast,Arcane Blast,Arcane Blast,Arcane Missiles
/cast Nether Tempest
/cast Mirror Image
/cast Arcane Power
/use Brilliant Mana Gem
but the Arcane Missles seems to get cut off still (and doesn't fire as often as it should).