Apparently you can use [nochanneling] by itself to indicate ANY channeling. More useful to warlocks as they have multiple channeling spells like Drain Life, Drain Soul, Drain Mana, Hellfire, Rain of Fire, Health Funnel.

So...

Code:
/cast [nochanneling] Mind Flay
...should work as well if you don't want to interrupt any channeling you might be doing.