This is an interesting idea. But speaking from one who owns an SG09. I'm not quite sure this will work. There is literally no room behind the PSU unless you maybe go ITX.
The 24pin is right behind the PSU. I can't say for sure about a second 120 fitting there with matx. But I'd highly doubt a 140.
If you google SG09 one of the first pics that show is it with an intel watercooling unit. That picture shows very well how close the PSU is to the MB and connections.
One option I could say is I saw someone mod a dual rad into the bottom. It may be possible to add another rad there easier. But you'd have to make sure it wouldn't interfere with your GPU and its cooling.
Heres some threads I found before I went with air.http://www.overclock.net/t/1348752/build-log-watercooled-sg09-sff, http://forums.bit-tech.net/showthread.php?t=256575,
I hope some of this helps. And I wish you luck. Make sure to post pics. I'd love to see it!