Nope, it's a passive, the attacks always splash, as soon as you unlock the W.
Hmmm, Sheen is interesting, still think I'd go for the chalice of harmony early on. And the ability I do spam is my E, Q and W are kept for when the situation dictates it, although I do use Q a lot against minions to help with the farming.
I should probably build a mastery page specifically for him, like I have on Janna.
But then again, on the chalice... maybe the philosopher stone is the better choice, as it helps with money issues and mana issues. I'd go for the Miracle however, as I have the nasty habit of forgetting about my active items. (If I could move them to 1 2 and 3 it would be simpler, but when an item is on 4 and 5 I hit R by accident once in a while and that sucks.)