Wait, there are those guys who make heatpiped 1U racks, who were they ? Saw the link on these forums.
On VH cool case gallery i saw a 19" 2x2U config with the PC in one enclosure and WC equipment in the other one. So this is definitely possible.
(going to look for those watercooled racks, i saw them i'm positive about that)
(edit) yes!!! Found em:
http://www.calmpc.com/english/product-2-e.htm
(reedit) hm my bad it's a koolance look-a-like.. hold on i've not given up.
* Not watercooled, but good already:
http://www.carillondirect.com
* Ha here they are:
http://www.signum-data.de/english/index_eng.htm