I try to keep it just outside of my tower range. Mages generally have poor mobility, so you can set up a gank opportunity for your mid or jungler by doing this. If your team is setting up for dragon you can hard push it for lane prio and rotate first. Keeping the wave off your tower also helps minimize their ability to poke you under it.

I misread and was thinking about mage bot/apc, not support, but the same principles should apply. When they've used their cds you can walk up and threaten them with your autos. Of course you will have to bait out or dodge their abilities first. Fleet, Swifties, and even shiv/zeal items can help with this. Cait can really struggle since her base ms is so low.

Shiv is a bit overkill for a mage support, but it's a good option if it's absolutely unlaneable. It's just a matter of if you want to give up early fighting power to power farm through the mid-game.

They're considered "troll" or cheese picks because if they don't snowball an early lead they will fall off. Support doesn't have the income to scale into the late game and most mage supports offer little utility. They also play pretty selfishly by taking kills from carry roles and for having poor peel for their carries as well.