Mechanic idea

I know you usually post ideas to concepts and creations, but I don't see much interaction there and I wanted to get an opinion on an ability.

So you know how wards need to be hit a set number of times to be destroyed? What if there was a champion who could temporarily replace their health bar with Ward health? They would become immune to the damage (but not added effects like CC or slows) of abilities until you would take down the tics, but it would decay overtime (so they wouldn't have it up permanently).

I was wondering if this would work as a psuedo aggro mechanic. It would force targets to take down the tics if they want to hurt you, so if placed on a tank it would force their auto attack centric to focus the tank.

Stupid idea? Toxic? Has Riot tried something like this before but didn't like how they implemented it?