I fully understand the goal of your post. I downgraded to 2.09 and stayed there; never installed 2.10 again. Until I read Upton666's post about how to resolve 2.10's issue. I decided I was going to try the steps for myself. Then, when I ran the App Store (i.e. Software Update), I noticed 2.11 was available. So I thought: heck, I'm just updating straight to 2.11, and succeeded. Even thogh SU then reported 2.10 to still be available for installation, when I inadvertently clicked the Update button, the rest of OS X apparently thought otherwise. 2.11 was not actually downgraded to 2.10.
If I knew in advance how to Hide Updates in Mountain Lion, I would probably have taken that short cut. However, Google failed me on this occasion. That's where I thank you, Gaget, for telling me how to do it in Mountain Lion. I shall remind this for when such a case shows up again.