If I'm not misunderstanding you there should be a a couple of ways to do this inside Studio One 5 without needing any 3rd part plugins. I also added pictures to help show how to do this.
1st: This first one you would just use binaural pan twice in this order. Hard pan the first one to where you want and the second just becomes your mono. You also could then bounce this out to make it a mono file.
3rd: Another way to do this would be to directly change the audio channel to mono.
Bounce out if you would like to see the change directly in studio one.
Another way I know how to do this with 3rd party plugins is using ProQ3 form FabFilter. Just click that L/R
Notice it changes to a M/S Mono / Stereo. Just pull the slider back and it reduces the stereo from the audio.
You can also do this directly with Fabfilter ProQ3 by change the bands, but come be a little complex for a simple task.
Just a heads up, My bad if I read your question incorrectly and gave the wrong help.