Build directory and executable to be run should allow environmental variables to be used in path

Currently I delete the default build steps and specify my own make commands to be executed when I build(Ctrl+B) from qt creator. I also specify the path of executable to be run when I press F5. I specify 2 things: build directory,executable to be run. Now I don't want these to be absolute paths. Instead I would like to them to in terms of environmental that is set up by user appropriately. Ex : the build directory could be: $BLDDIR/bld/qwave and executable to be run could be $BLDDIR/bld/qwave/qwave. Now user can set BLDDIR to whatever value he wants before he starts qt creator. But the qt creator doesn't allow this. It says $BLDDIR/bld/qwave path not found and $BLDDIR/bld/qwave/qwave executable not found. Although I can see $BLDDIR setup up nicely in the list of environmental variables shown in Qt Creator.