What if we made Rammus's 'w' a toggle ability?
Instead of defensive ball curl lasting for 'x' number of seconds, Rammus now gets to choose how long the ability is active. Rammus can spend a certain amount of mana (possibly increasing overtime) to maintain defensive ball curl. Basically, Rammus is now in control over how long defensive ball curl lasts, as long as he has the mana.
excluded for obvious reasons, but hey it's their job) and if he could keep it up for a long time he would be too strong during teamfights, managing when and how use the W is a bit of skill play by him and counterplay for the enemy (a bit like Swain ult - if you get him when it's down he's dead).