In fact, this is a hard problem. I also tried to get the solution. But what I can do is just a little in Reflection condition.

Here is my idea:
1) complete what u want to animate in the sence;
2) save the sence as another one;
3) make the camera in the sence reflect it's position againt the mirror and hide the mirror;
4) render the two sence respectively;
5) use the compositing software to composite the two animations.(According to geometry, the latter animation should contain the image in the mirror of the original sence but just in reverse. )

Unfortunately, I have no experience in this cast. So if you have no idea and have to go through it, try it.