Regarding the existing Prism2 driver, its author wrote:

"In theory you should be able to use the native MorphOS version of prism2.device 1.x (the WEP-only version) [...]. MorphOS probably doesn't have a card.resource for the Powerbooks' PCMCIA/CardBus slot, but if it did you could perhaps use the 68k WPA prism2.device."
http://www.amiga.org/forums/showpost.php?p=696038

Interestingly, the MorphOS 3.0 release notes read:

"Fixed to map Cardbus units of PowerMac and PowerBook computers."
http://www.morphos-team.net/releasenotes/3.0

Maybe this amounts to something? Although I believe it still lacks the required card.resource.