I made a mistake in my wording. Instead of "animation be played when casting a projectile", I should have said "after casting a projectile".
My plan is to already have a casting animation of the character. Afterwards, a bolt of lightning is projected from the character in a line (but I need the lightning to stay still as it progresses through its animation). If a target is in its path, it will be hit by the invisible projectile.
I can do this with casting animations, but my cast time will be about 3 seconds, therefore the lightning animation would need a lot of blank space at the beginning (about 2 seconds worth) whilst the actual lightning animation will be 1 second long... the projectile will then instantly be released after that 1 second.
I hope that makes sense... does that seem like a decent approach? It seems like a "hackey" solution but I think the only available.