I have answered a similar post on :
Finding Bluetooth link key in Windows 7, to double pair a device on dualboot computer.
That post was for a similar problem when pairing multi-booted Windows 7 and Ubuntu,
and the question was where does Windows 7 store its passkey,
which is the 128-bit key that the devices exchange during pairing and use thereafter to encrypt all their Bluetooth traffic.
My answer at that time was to look into the registry key at :
This key is protected and one has to change its owner to Administrators to access or even see its sub-keys.
In theory, if you pair the device with both Windows installations and then
transport this registry key from the last-paired to the other,
then both installations will be
identical from the point of view of the bluetooth devices.
However, I do know that in Windows 8 many changes were done to the bluetooth protocol,
so this is not guaranteed to work,
but it would be interesting to see if this technique is still useful.
I suggest taking precautions before modifying the registry,
at least to create a system restore point.