Yes, in cases where the tool can't find the mirror automatically you can edit the pose.
- You would mirror the pose... which will create the bad right pose, but at least it gives you the pose node, on the proper joint etc
- Select the new pose, created after mirroring... it might already be selected
- In the maya viewport position the controllers to the proper mirrored pose.
- Right click on the mirrored pose and select update controllers. This will update the right side pose with the mirrored pose you just edited in maya
- select the left pose again and hit mirror to fix the mirrored pose.
Moving forward after this, if you make an edit to the left side, you can hit mirror button, and the pose should mirror better to the right side.
We've been using this recently in Method Montreal, and can confirm that this workflow works. It seems like a lot at first but after you do it once or twice it's not too much work. If you have trouble following these steps, I could probably make a video.