Interesting article: I'd never heard of patron-driven acquisition before, but the basic idea is one that other services could borrow:
[L]ibraries will load a selection of records for potential titles into the library's catalog. When a user discovers an item of interest, they'll be able to explore the title at no initial cost to the library. After a certain amount of use, however, a purchase is triggered, and that title is added to library's collection, charged as either a single-user access price (usually list price for an ebook), or the higher multi-user access price, depending on the preference of the library and on the availability restrictions put in place by the publishers. Crucially, the process is automated and seamless to the user, who is unaware of the transaction.