What I do is a trick I learned right here on Mobileread.
I download the library book to my Sony 505 and then change the date on the Sony to 2008 instead of the current 2009. Be aware that if you sign back into the Sony Store or Adobe Digital Editions, it will change the date and delete your expired book. I forgot and did that one day without thinking. Changing the date on the Sony does give you time to get that book finished.