It's not that simple.
qmake.exe has paths, ABI, mkspec, etc., all hard coded in the executable. Run something like "strings qmake" and grep for one of the settings obtained by "qmake -query". They're in there.
Specifying a mkspec in that dialog does not do enough to solve the problem. In fact, even though my kit has my Linaro cross compiler set up, it still calls MinGW's compiler and I end up with a Windows binary.
The qmake settings can be modified (using "qmake -set"). I tried to take the MinGW qmake.exe that is installed with Creator and change its settings to match those from the Linux build, but this does not work.