I used to do this but even if it's automatic, the income is to low.
I wasn't using TweetFeed (never used it) but I was using WP Rss Poster and AdFly Wordpress plugin.
AdFly can convert all your outgoing and internal links using the API, and Rss Poster has options to shorten the links that it Tweets, and bitly is one of the options. So there you have it.
It will Tweet the shortened AdFly links with Bitly
Have fun