This blog post might help https://blog.torproject.org/blog/experimental-defense-website-traffic-fingerprinting it's not specifically on correlation/timing attacks but it contains the following sentence:
the researchers point out that a Firefox addon that simply performs background HTTP requests concurrent to normal user activity was enough to foil their classifier.
I did some digging to see if I could find such an add-on and I found this. http://www.instructables.com/id/How-to-generate-fake-traffic-using-the-Tor-Browser/
Using the Tor Browser go to the following Mozilla plug-in recourse center and download the reload every plug-in:
I went to the add-on page and typed in "reload every" and it was the first result. I haven't tried it yet but you can set a time (the minimum seems to be 5 seconds) and the add-on will reload the current page every set number of seconds. Opening something like Wikipedia in tab 1 and reloading every 5 seconds while you use other tabs for the tor traffic you are trying to protect seems like a decent way to use this. If you want to generate more traffic you should be able to make the add-on reload several tabs at the same time.
Not sure if this is exactly what you are looking for but if it works like I expect, it should fall under the category of the "replay traffic going through Tor" part of your question. I couldn't find the name of the add-on that the blog post was referring to but perhaps there is an even better add-on that I didn't find.