Struggling to export Mono as Stereo

Hello all!

Please help me figure out the error in my workflow.

For example, at events, I've been recording the wireless mic feed of a speaker into Channel 1 of my Canon C100, and recording the ambient room sound with the internal mic on Channel 2.
I bring my footage into FCPX, and begin building my multicam clip for a stringout. Multicam as follows
Angle 1 - C100
Angle 2 - 6D
Angle 3 - 70 D

So far so good. I have a synced multicam clip that I use as the basis for all editing. To only hear the Mic, I select the C100 footage (which is the selected audio angle for the entire event), set the pan mode to Stereo Left/Right, and then the Pan Amount to -100. At this point, all I hear is the lav, coming out of Channel L. Because it was recorded with the C100, its showing as being part of the Storyline for Channel Configuration.

When I go to export the project, I would like to have the lav audio exported on both channels. No luck.

Any suggestions? Thanks in advance.