As far as I know I don't believe it's possible. If it IS possible you would need the appropriate daughterboard (Airport & wifi are on the same card, I believe), power/data cable between the motherboard and daughterboard, and internal antennae.
It's interesting to me that Apple doesn't say this model iMac "lacks Bluetooth" but it actually "does not support Bluetooth". This leads me to believe that the required interface on the motherboard for the Bluetooth daughterboard may not exist, and/or Apple has a software block in place to prevent the Bluetooth kernel from loading on this model.
It would surely be a lot simpler to use a Bluetooth USB device.
Questa risposta è stata utile?