I'm compiling on Mint 14 (which is based on 12.04) and I installed Qt5 from download
here (I didn't compile it).
I didn't even bother with symlinks I just set the PATH so that it picks up Qt5 first and cmake does the rest. Also, I find setting the LD_LIBRARY_PATH isn't needed so long as the path to the Qt5 lib directory doesn't change.