Just for kicks, I went ahead and unplugged the internal bluetooth card on my 5,1. (Be gentle pulling the plug off the card) I left the OEM BT card and antenna in place and plugged in the iogear bluetooth USB adapter. (IOGEAR IOGBU521 Bluetooth 4.0 USB Micro Adapter)
Upon reboot, my BT keyboard, trackpad and magic mouse reconnected without issue. Pretty good!
Might investigate the continuity activation tool.
Apple Bluetooth Software Version: 4.4.3f4 16616
Hardware, Features, and Settings:
Name: ChungMacPro
Address: MAC ID removed here
Bluetooth Low Energy Supported: Yes
Handoff Supported: No
Instant Hot Spot Supported: No
Manufacturer: Broadcom
Transport: USB
Chipset: 20702A3
Firmware Version: v14 c4096
Bluetooth Power: On
Discoverable: Off
Connectable: Yes
Auto Seek Pointing: On
Remote wake: On
Vendor ID: 0x0A5C
Product ID: 0x21E8
HCI Version: 0x6
HCI Revision: 0x1000
LMP Version: 0x6
LMP Subversion: 0x220E
Device Type (Major): Computer
Device Type (Complete): Mac Desktop
Composite Class Of Device: 0x380104
Device Class (Major): 0x01
Device Class (Minor): 0x01
Service Class: 0x1C0
Auto Seek Keyboard: On
Let's see if it fixes the notorious battery drain issue with the Magic Mouse on my Mac.
Edit: It seems to fix one annoyance: occasionally the Magic Mouse will disconnect with the original card if I physically disturb the mouse violently (almost as if the battery has shifted causing a disconnection) but the iogear adapter seems solid. Nice!