use libs from different paths for different build settings

Hi,
I'm new to QTCreator. I'm using QT4.8.1 and QT4.7.1 on Ubuntu. And I'm new to Ubuntu, too.
With QTCreator I made a SharedLibray. I use shadow build and have one output folder of each Build configuration. That means I have 4 output folderutilities\Qt_4.8.1_debug
utilities\Qt_4.8.1_release
utilities\Qt_4.7.1_debug
utilities\Qt_4.7.1_release
Each has a file named libutility.so.1.0.0

Now I'm implementing a Testprogram and have the same 4 build configurations like in the lib project.
The Testprogram has 4 build configurations
Qt 4.8.1 Release
Qt 4.8.1 Debug
Qt 4.7.1 Release
Qt 4.7.1 Debug

Now I want that if i compile and run the Test program with build configuration
Qt 4.8.1 Release it should use the lib at the folder utilities\Qt_4.8.1_release
Qt 4.8.1 Debug it should use the lib at the folder utilities\Qt_4.8.1_debug
Qt 4.7.1 Release it should use the lib at the folder utilities\Qt_4.7.1_release
Qt 4.7.1 Debug it should use the lib at the folder utilities\Qt_4.7.1_debug

I tried out the 'wizard' like it is shown in the QtDocumentation but it don't work.
I know that I use something like that in the Test.pro file:

LIB_SUB_DIR =lib

CONFIG(release, debug|release){
LIB_SUB_DIR +=_rls
message(tralli tralla)
}

CONFIG(debug, debug|release){
LIB_SUB_DIR +=_dbg
message(Hib Hib Hurra)
}

but this differs only between release and debug.

What musst be done to get different folders for the QT4.7.1 and Qt 4.8.1 build setting. I have no idea what to do.

Thanks