Are you sure about that? It was my understanding that although the "Enterprise Activation" procedure is run, it runs over-the-wire if the Blackberry is still tethered to the USB port, and switches to over-the-air if you disconnect the Blackberry.
Certainly my Blackberry Router status shows a lot of data packets moving back and forth if I do an Enterprise Activation while connected... I'm certainly hoping that the device isn't just engaging in idle chit-chat with my BES...
EDIT: In fact, this must be the case, since I've successfully completed a full Enterprise Activation while connected to my USB port with the radio on my BB turned off.