If you do put the source in another location as I did, it will impact a number of items:
You can solve this problem by using symbolic links to folders.
The idea is to have one "main" folder (c:\qt\qt) which is in fact a symbolic link to the version of qt you're using at the moment (c:\qt\qt-4.5.2-gcc3, c:\qt\qt-4.5.2-gcc4, c:\qt\qt-4.5.2-vc...).
To be able to quickly change current version of qt you can create a series of batch files using junction tool from M$

Each batch file consists only from one line
junction c:\qt\qt c:\qt\qt-[some version]

You can also use this approach when you have more than one mingw version to be able to switch among them easily.