@monster, it's cool, but a cele 400? It's like the passive (no pump) WCin with a K62 350...while cool ideas, not really useful with a Barton 2500. Neat, though
If burying something (like Blade & a few others) isn't possible- and it really is the best passive method- that you're of course looking at passive radiator design (or a bucket). I've tried a few, but what I've found works best is
Gerwin's idea. Spirals work ok, too, when used in addition to my Gerwin rad my huge coil dropped 8c off my T-Bird 1.2.
Gavin did a mighty fine job with it.
I think you may be thinking of something like
this...I'd drop it in favor of a cheaper cu pipe solution, if I were you, but I love to see new stuff

Also something to consider would be a real radiator, not a heater core, from a truck or van.. like
here. Just ideas- I'm sure your own will blow all others away
Cheers