Saw a couple of Zalman 7000's up cheap today (damaged packaging), and noticed that if you removed the fan from the second one, turn it upside down and solder it to the first, you would have a fantastic heatsink with very little extra airflow resistance, anyone tried it?
Even better would be a version with a hollow centre to the fan so that you could run a short heatpipe up to the centre of the second H/S.

Bit hard to follow, but if you get what I mean, I reckon it would make a fantastic HS?