Using Liferea’s ability to locally parse feeds and a little inspiration, I hacked up a sed script to make my twitter feed all pretty. It works great for me, YMMV.
I published the script here, under the GPL. To use it, save the source into a file somewhere, make that file executable, then choose “Use conversion filter” in Liferea and select the file you just created. If you have problems, you could try leaving a comment here, I might be able to help.