I don't have wavelab on my lappy, so I can't tell you the exact process, however I think I can explain from memory.
First, open a new project, split to mono. First with one source, then the other. Probably under the process tab, not sure though. Then, import each individual track into montage under mono import option in montage. You can pan mono sources, but not stereo sources. Make sense? Then when you have it all panned correctly and mixed to your liking, render it to stereo.
Hope this helps.