As mentioned at The Adult ePub Library, there is a lot of services which converts online text to ePub format for easy viewing on a e-reader. The only drawback is that a lot of stories on asstr are in clean .txt format with forced line breaks. None of the converters can strip away the forced line break - instead they preserve them using <br /> or <pre>
In order to convert fixed-width text to an e-reader friendly format, I have created a bookmarklet. Right-click the link below and choose 'Bookmark This Link':
Bookmarklet: Fixed-width fixer
Whenever you are viewing a story with a fixed width, simply click on the saved bookmark to convert it to free-flowing text. Try it out with this one: http://www.asstr.org/~Kristen/01/voyeur.txt
Instead of using the bookmark, you can also paste the URL of the fixed-width story in the input field below. It will then be converted to free-flowing text: