Area of Effect: Display Markers

[Tetsaru]

Holding the button brings up the AOE target, releasing it casts the spell.

If you have enough time to consider radius, you have enough time to hold the button.

That, or, if it's a move that hits everything surrounding you (like Blizzara), you could just hover your cursor/mouse over the spell's icon, and the AOE ring would show up then before you actually set it off. I've seen League of Legends do it that way for certain moves.