Cool way of making units appear they're casting?

When you add casting times to abilities, they just stand there for X secs THEN do whatever ability. I want the appearance that they're channeling a spell or ability. For instance, a mage is casting a firebolt but the casting time is 3 secs before the effects goes off. So in that 3 secs I want the mage look like he's channeling the spell with some sort of effect or animation of the mage concentrating or something. I just want some indication that a hero or unit is casting rather than just standing there. Thanks for any help.

Special Effect - Attach Special Effect on Unit

I believe that this has something to do with the "Art-Animation Names" section on the object editor, you may see that the chaneling spells, like blizzard and rain of fire, under this section there is "spell" and "looping".
Or it has something to do with the model that you are using...
I am not sure, but it can be, maybe.

I tried that, but even when i use the - Begins casting an ability function it still only attaches the effect when the casting time is over. So they just sit for X secs and do nothing for that duration.

Did you try the Starts channeling ability event?

Haha, I feel stupid now. Thank you for pointing out the obvious freek :) Works perfectly now.