When exporting into .wav or .mp3 you will loose surround sound data as those formats don't support it.
Realistically you want to do your work in the stereo spectrum to be able to export.
To achieve your desired results (depending on what product you're using) double click each track and bring up the mixer. Then use the the pan knobs on each track's strip to pan one track left and the other right. This will allow you to do what you want and export it.