A PAN (Personal Area Network) is the missing bit I couldn't figure out so early in the morning. When you create that, the Property offering "Allow this device to wake the PC" will be visible.
Go to Control Panel>Network and Sharing Centre then click on (Set up a Broadband, etc ..... Quick Access and that last bit is what you need to accept.
Once the BT device can scan for the PC and find it, you're nearly there.