Not in the game, AFAIK. You can get a stereo to mono cable adapter, or use headphones. Partly pulling out the audio jack may get it switched to mono, as well.
In Windows check if there is a mono setting if you right click the speaker icon, select Playback Devices, then the device and click the Configure button. There probably isn't, but you may get the same effect by right clicking the playback device, selecting properties, then in the Enhancements tab enable Room Correction. A quick search brought up mention of
Virtual Audio Cable, but I'm not familiar with it, or the limitations in the trial version.