I did this very thing today. As Taric, my pokemon Lucian ended with S+.
http://img3.wikia.nocookie.net/__cb20131127012039/jjba/images/4/43/KarsExposed.png
+
+ 100 souls + Dark Harvest
What ADC?
I'll just be over here getting my consistent S grades on sona...
ouch that hurts a little too much
I remember back before they made it so kills and assists are weighed equally for a support, so if you had a bunch of kills on support you'd get S rank. My friend was trying to tier 7 his supports so I'd let him have all the kills and solo tower golds while I farmed. I'd also sacrifice my KDA to save him from dying if I could. It was pretty funny, but also sad because sometimes even that wasn't enough.
I tried to Tier 7 Leona and it was ridiculous, I could only die once a match if that, and I had to have absolute vision control everywhere at all times, but the only games I could even get the vision score I needed were the ones where the enemies were actually warding, and a lot of the times they weren't because we were winning lane so hard and they had no chance to without just instantly dying.
I also just had a Vel'Koz support game where I had over 66% KP, 0 deaths, and the entire river was lit up for 12 of the 17 minutes. I only missed a single digit amount of skillshots, even though I know that's not actually counted as a metric, but still. I only got an S, not even an S+. I don't know if I just don't know what metrics supports are graded by as well as I know the ADCs, or if it's just that ridiculous to get.
Honestly, I find support the easiest role for getting an S. The only thing you need to focus on is not dying more than 3 times, getting as many assists as you can, and 3-4 kills, not more. I think the only support I didn't have an S on was Alistar, all the others were fairly easy. Getting S on Vayne, on the other hand, hard as hell if you don't have a decent support.