Looking for and LUA Condition to detect a GCD and then Cast a spell that counters the GCD.

You mean like how heroic strike is off the GCD for warriors?

yeah and Empower Run weapon is off the GCD for DK's

I believe my warrior fight class in my package still has a work around for heroic strike in it.

I add a spell called CastSpellByName("Faux Heroic Strike"), add in conditions like if Rage > 100 blah blah, then I add in CastSpellByName("Heroic Strike"), finally I add in a condition that is impossible to meet, something like if health > 2000. Make sure you select the appropriate options to run it as LUA and not check if you know the spell and boom, it fires off during a check for conditions instead of firing off as a spell.

Ok im not totally understanding what you mean?

I don't have my computer set up quite yet, so I can't give you an example just yet, I'll post it sometime tomorrow after class though.