With the CodyHouse team we have been spending some time thinking about how to make the back-to-top button "smart". If the goal of the user is to get back to the navigation, why don't put the navigation where the back-to-top button is supposed to be.
We come up with a new interesting UX solution, that can be downloaded for free on Cody.
Here is the demo:
http://codyhouse.co/demo/smart-fixed-navigation/index.html
Finally we created this animation (kudos to @[442518:Gabriele Mellera]) to show the idea behind this code snippet.