Will refer to Premiere Pro as PP and After Effects as AE from here on:
Here is a solution which requires AE that I think works but can't test it because my demo of PP and AE has finished. Luckily for you, they have trials for many products including AE which you can download from their site. I contacted a friend of mine who works as a video editor about this and he mentioned something that sounded a lot like this method, but without the conversion I will mention. At least I'm pretty sure since some of what he said went over my head.
Anyways, he initially said that .ass files are not compatible with Premiere Pro. Luckily though he pointed out that you can easily convert .ass files into .srt files, which can be imported into PP (CS4 and above).
Here is a website that does this for free
This is where he began to loose me, but mentioned using the analyze content feature to make sure the content roughly matches up with the video. The video below will explain more and clarified stuff for me.
Here is the video explaining how to do this and how to automate the process