Is the back of your case like this?
http://forums.overclockers.co.uk/showpost.php?p=8120432&postcount=16
You can fit 2 rads there, but beware that thermochill have wider fan spacing than others and won't aline to your case holes.
Either chose a lesser rad,
or drill new holes in the case to line up with those on the rad
or get a "120.2 rad grill with mounting holes"* and cut some of the case out at the back.
*google for "that above"