molak: yeah, that could be a good idea. I'll consider it as an option if I want to build something more "extreme" in the future.
Thanks for your input, guys. I'll go with a passive solution for now and I'll leave trying exotic stuff for later.
I'll actually make my rad from copper tubing. Which brings me to this question then: Is there any kind of special copper that is flexible enough to be bent into circles without causing weird stuff to happen to it? I think I've seen such tubing at a Home Depot style store here in Canada and it seemed flexible enough. It was about 7$CAD for 10' if I remember well (there was 25' long tubing as well). How long should be enough? What diameter is ideal for, say, a 1/2" system?
I'm thinking maybe I can buy two 25' long "rollers" and use them in parallel like a setup I've seen on the internet somewhere.
I'm ordering the pump and water block today, too.