I have an 80/20 solution of my own for keeping my 505 safer. I found a book at a garage sale that had a thick, well-padded and plasticized cover - It is just a little longer than the 505 in its cover. The subject matter of the book seems like something no-one would want to steal!
It is actually a book of blank pages for a mother to write memoirs etc.
I gutted the book and used book-repair tape to smooth the inside. I didn't like the idea of the usb port etc. peeking out the sides, so I ran up a little bag on my serger that fits the reader loosely. I tucked the reader into the cover and put a couple of rubber bands on it. Very secure! I can also read using the book-cover if I tuck the cover's sides into the rubber bands. I just wanted to be able to put the reader in the side pocket of my purse without it being a beacon for thieves. I don't think anybody would steal this girly-book!
I could have gotten more fancy and put in sleeves on the inside for the cover flaps etc. but that would sort of defeat the 80/20 idea. This is good enough for the moment until I find the EXACT thing I want!
Hope the pictures attach okay.