Well, Ambicom got back to me, with a doubtless business-wise but somewhat disappointing reply. They indicate that the WL54-CF uses the Marvell 8385, and that's all they can provide in the way of help.
I've also searched the forum and googled quite a bit, without hitting on the 2.4 driver.
At this point, unless there's a path forward along the lines of a) finding the 2.4 driver, locating help to create the driver, or c) potentially contactin Marvell for help, I'll need to return my card and look for another solution.