This topic do exactly what you asked for without rooting, I did it on my PRS-T1 successfully months ago.
It doesn't actually modify any software but puts instructions in the books database that changes the time of book addition to the reader inside the database each time a book is read, making that book the most recent addition to be displayed on the home screen.
Look at #11 post for detailed instructions on how to apply the modification.
However, if you add new books to your reader, they still shift/replace your most recently read books on the home screen (and the next book you read will replace them again).
Didn't tried with last firmware (1.04), only with 1.03.
WARNING: you need to apply the modification both on the internal memory and the micro-SD cards (if you have one or more).