Select the object, and type Alt + K. The object will be transformed in two mono objects on 2 different tracks. These objects are paned in the center by default. If you play the 2 tracks, it sounds mono because they are centered. After you can pan right or left, as you want.
If you want to get a mix in mono, export as *.wav and select "mono" instead or stereo. You can re-import this file in your project.