I was wondering the same thing a couple of months ago, but I never got around to researching it. I imagine we would have to rig up some kind of pump to run the fluid through the cooler. My T5 was making a lot of heat when I was driving the mustang recently. The 4 catalytic converters don't help either though.
I dont see a need personally. There is no pressurized fluid, like in an automatic.
It would be easier to run a synthetic, which should more than take the heat.
A 180* motor expels a lot of heat too, but it is barely entering its warm operating threshold (meaning that heat coming from the trans tunnel does not indicate a trans is running too hot - it just feels hot to us).