Github: Mirroring gh-pages to master

I'm developing a jQuery plugin that's being hosting on GitHub. It has a demo included of which I'm manually copying and pushing to the branch gh-pages, what I'd like to do is have it so when I push a change to master it is automatically pushed to gh-pages, or at least a setup where they are mirrored.

I've already seen this question but not sure if it really answers my question with regard to these requirements:

1. I use Tower, I don't mind using the terminal (Mac) to make changes to config, so long as the solution works with this GUI.
2. I only want this 'mirroring' on certain repos, not on all of them on my machine.

Cheers