Scale bones of an animated FBX

Hello! I'm making a 3D Character Editor, as the City of Heroes, Champions Online and other games...

I got a trouble by scaling the bones. I can scale them with my slider if my character isn't playing animation. If he is animating, i cannot do it.

I would like to use these scaled bones for a super customizable editor. But i cannot use a different scale of original character if he is playing any animation. How would you solve this? Can you help me?

Thanks for help! :D