I know this post was from a while back, but I’m working on a similar problem and I thought I would mention that, in the editor Animation mode, there is a poses tool that lets you save and paste poses to selected control rigs. With the poses tool you can also mirror paste the saved pose onto a control rig.
However, I have only had success mirroring poses using the pre-built control rigs for Manny included in the 3rd person template. I have not been able to accurately mirror poses on any control rig I build myself. A similar unresolved issue was mentioned here.
If anyone knows how to make a control rig respond correctly to mirror pose pasting with the pose tool I would be very grateful for the help!