I had a suggestion. Which may strike some as extreme laziness on my part (which in fairness it is laziness).
I have three overdue books to return. Mostly because I have been too lazy to walk down Dartmouth Rd to return them (I should really say I haven't had the time)
How about a Library 'book drop' by the station, where people can drop off their overdue books in a secure box--like a post box. The library in the town I grew up in had one near the centre of town. My mom used to use it frequently.