yesh i just had a look myself at the developer manuall for the ibook G4, it says:

USB 1.1 Controllers The external USB interface is via the PCI USB controller; see “PCI USB 2.0 Controller” (page 30). The Intrepid IC has three independent USB 1.1 host controllers each with a maximum data rate of 12 Mbps. The controllers comply with USB Open Host Controller Interface (OHCI). In the iBook, only one of the Intrepid USB host controllers is used for the Bluetooth adapter. The other host controllers are disabled for power savings reasons.

so yeah in theory you could attach a bluetooth module to the internal bus if you could find some space for it. I'm going power down now and have a look!
I break stuff.