A correction at Jane’s post about the Bluefire Reader states that, after all, it cannot yet do DRMed eBooks from public libraries as I initially thought.
The Comments there lead to a Mobileread thread where Micah from Bluefire confirms it:
Your Library books may not be transferrable to enable the “early return” option. To read them in BFR, you would need to download them directly to the device. This is possible with BFR, but unfortunately at present this requires that a library make a specific type of link to do that (easy to do, but Libraries are not particularly nimble at times). We have an idea that may work so that they don’t have to do that. May be in the first update (very soon). I’ll post on that as I know more.
So … close. But not yet.