All the adapters Ive seen/used needed the USB for the BT to work, otherwise only the wi-fi will work.
The SFF doesnt have an internal header, but you can just route a cable out the back of the case (that's what I did).
The Other form factors may have an internal BT header??
I think the reason the Fenvi is mini tower only is due to the slot size, the BCM option comes with both full and half back plate adapters so they will physically fit in the case. I believe they will both need a USB connection for BT to work.