Controller Customization without Big Picture

Description:

This feature has been lacking in my opinion, and I don't think it would be hard to implement. I feel that you should be able to customize your controller buttons and settings in the normal Steam Overlay (not using Big Picture) because there are some games that I just want to pick up the controller and play mid game.

Example:

I like to drive using the controller in GTA but I like using mouse and keyboard for everything else, so I should be able to start GTA without big picture, start playing and when I want to use the SC I should be able to open the Steam overlay and customize the controls from there. I understand that you can use controller mid-game but you are not able to customize the controls.

Anyone else feel this is a necessary feature?

TL:DR I want to be able to customize controls in the Steam Overlay without having to use Big Picture.