Hi all!
A first compiled rough version for the PRS350 is online. Feel free to give it a try:
http://erhartc.bplaced.net/ereader/index.php

New features:
- Changing line-height and font-size on the fly in most EPUBs
- Changing allignment (left, center, justified) & text-indent over options for most EPUBs
- New font-size-overlay
Source-Code (forgive the big mess inside the code...) online.
A.
Edit 14.04:
New features:
Changing reader-interface-font
Flexible way tuning CSS-tags