Then just disconnect drive B during the "interrogation"and downloading on drive A.
End of worry about Microsoft spying.
Gee - you could probably do something like that with a 200+ gig hard drive sitting in an external case on USB.... ;)
This supposes that nothing is happening in the background while the B drive is connected. It could be sitting there doing a scan every X minutes and storing that to Drive A. In fact, it probably is.