I tried; it installed for CS5 only (exactly what I didn't want it to do). I don't see where the app/plugins are stored on the computer, so I haven't tried to manually fix it.
I'd like to have my old version of ACR back for CS5, and to be able to use the new one in CS6 beta.
You cannot install 6.7 in CS6. It is specific for CS5.
If you are interested by the additional camera support, I suggest that you convert a copy of the files with the DNG converter 6.7 until Camera Raw will be updated.
If your camera manufacturer supported DNG as a native raw format, you would not have this issue. (And I can't imagine what the ACR/Lightroom and other teams would come with with the time they would win thanks to that.)