creating a child theme/template

We are using the BuddyPress Social theme at QuieroQueSepas.US, I did not see it in the choices above so I picked the one that sounds the closest to it. We are using webuzzapps to customize our facebook page, which allows us to create a link to a page on our site that iframes the page into fb. The only thing is, that the width needs to be 520pixels for it to look right.

I'd like to know if there is a way I can create another template which I can choose from in Page Attributes that will fit the parameters of FB? How do I go about it?