Check out the PRS+ thread here:
https://www.mobileread.com/forums/showthread.php?t=64510
PRS+ is some kind of Firmware replacement which adds more stuff to the reader. I'm not sure what the latest updates bring, but I think that I saw what you're looking for. Actually, I just checked the project page and the following are the latest functions released in a beta version:
•Localization (Catalan, Czech, Deutsch, English, French, ქართული, Русский, Spanish)
•page per minute / remaining time settings for PageIndex
•dictionary by Clemenseken & Lisac (to use it, put your dictionary files int /database/system/PRSPlus/dictionary. Dictionary files MUST have "dic" extension)
•Book History by kravitz
•option to set default zoom size, limit available zoom steps by kravitz
•Main menu customization by kravitz
•Introduced "safe mode", if reader is connected to USB during startup, PRS+ does not load.
•PRS+ settings moved to /opt0, PRS+ addons and core are now built into firmware
This is the project page of PRS+ where you can get more information and downloads:
http://code.google.com/p/prs-plus/