Basically what I do is have a macro like the following...
Originally Posted by Holyhunter
/cast A Murder of Crows
It will attempt to cast AMoC first, and it will no matter what cast Fervor right after. Say you are at 80 focus. You hit that macro, AMoC is cast and you drop to 20 focus...but since Fervor also gets cast in the same GCD you instantly bump back up to 50 focus and have enough focus in the next GCD for an Explosive Shot or whatever is next in your shot priority.
Say you have 20 focus. If you hit that macro, AMoC will not be cast, but Fervor will be. If you hit the macro again really quickly AMoC will be cast nearly instantaneously. I do the same thing with Multi-Shot and Black Arrow because they are close enough to costing 50 focus for me not to care that much. As long as you are managing your focus and not capping very often it is fairly safe to use Fervor in this way.