I am pretty sure /castsequence will not progress if a spell is on a cooldown timer until the timer expires. Someone can correct me on this if I am wrong, but this was one of the reasons I switched to /castrandom. Also, I don't know what happens when the focus target changes mid spell cast. Does it check the target for each spell in the sequence?? [edit: nvm, I don't think you can have multiple targets in a /castsequence as Ghallo indicated]

edit: Sorry, I just realized that you were trying to overcome this. What Ghallo pointed out is probably correct. The macro he suggested would probably work, but I don't think it will function any different than what Jafula suggested.