mudskipper
Ok, here are the instructions, first you install PRS+.
Then, unpack folders from "Universal Flasher 2.1" (
link) folder to your SD or MS card.
In folder files.505.1.0.00.08130\opt\sony\ebook\ delete subfolders
bin and
application.
Put your fonts files into FONT subfolder.
Plug the card into your reader, you should see Universal Flashers menu.
In this menu (I don't remember exact buttons) you should first select menu that creates new firmware image, then the one that flashes. (it could have been combined into one menu item, shouldn't be hard to figure)
Note:
The fonts, that you put into FONTs subfolder MUST have the following names (the fonts themselves, not the filenames, filenames actually do not matter)
Swiss721 BT Roman
Dutch801 Rm BT Roman
Courier10 BT Roman
Also note, that you can't use font files that are bigger than a couple of megs (universal flasher will warn you, if resulting image is too big).
In case anything goes wrong, don't worry, 505's are practically unbrickable.