Here is the beggining of a collection of tools (atm there is only one tool) to assist on animation
The version 0.10 gives the possibility of dealing with the knee pop, with it, you wont have a problem with this anymore :)
This was a 1h development, so its a little buggy and works only with autorig pro.
I plan to add more functions to it in the future (like a baking tool and rigify support)