Hmm...
tc-config seems to work on SNAT (MASQ) machines if POSTROUTING is
uses as FW_MARK_CHAIN in /etc/sysconfig/tc-config...
At least it should I think (according to KPTD 
http://www.docum.org/docum.org/kptd/)
Needs some testing on accuracy...

Uhh, I like this software, really...
I use it with pleasure on my access concentrators.
Make correct settings and it will do anything (ok, almost anything :) ) for you...

Vladislav