Hi Till,
there is not a real option for that yet.
Your solution is not bad.
I would make a link which links back to the "home" page and embed it via the footer (you can include a footer as a page under each post or page) or put it plain into the Custom Head section.
With CSS classes and page-slug you can define on which page the button gets shown or not.
Have a look here:
http://laythemeforum.com:4567/topic/1428/change-menu-color
You can also give the button a position fixed to always stay at the same place.
I hope I could help!
Marius