Help - Adding a Background Selector

I've been looking for a guide on how to do this so far I've got:

• Add Background Selector Panels from another skin with it
• Add Global Panels file from another skin with Background Selector
• Add Background Graphic files with name/numbering to match Selector Config
• Add line of code for the button to the Client Object Browser Panel

This final piece is the problem I have - Where in the code does it need to go and what needs to be added? Anybody got a ‘dummies guide’ or step by step to help? Every time i've found people asking it's like a secret topic where nobody really answers fully but several skins have it so it's clearly something people know how to make… 

I'm trying to update the appropriate code into this config file. Hope someone can help me out!