You can bind Win-B to tether Bluetooth.

 1. As suggested by [Techie007][1] you can create a shortcut by going to "Devices and Printers" right-clicking the phone and selecting "Create shortcut".
 2. Put the shortcut in a directory like "C:\Windows\BluetoothLink" by itself
 3. Install [Autohotkey][2]
 4. Right click on the Desktop, and choose "New" -> "AutohotkeyScript"
 5. Enter the following:

        #NoEnv  ; Recommended for performance and compatibility with future AutoHotkey releases.
        SendMode Input  ; Recommended for new scripts due to its superior speed and reliability.
        
        #B::
    	    SetKeyDelay, 200
    	    Run, C:\Windows\BluetoothLink
    	    Sleep, 300
    	    Send, {Down}
    	    Sleep, 200
    	    Send, {AppsKey}
    	    Sleep, 550
    	    Send, {Down}
    	    Send, {Down}
    	    Send, {Right}
    	    Send, {Enter}

 6. Save the Autohotkey script (e.g. Ctrl-S)
 7. Double click the Autohotkey script to run it
 8. Press Win-B, test that it works
 9. Open your startup directory (e.g. press Win-R and type "shell:startup")
 10. Make a shortcut to the Autohotkey script (so that it works even after reboot).

One could perhaps make this fully automatic by [scheduling a task on resume][3] but I am not sure I would recommend fully automatic Autohotkey scripts stealing control of your keyboard from you. They tend to be a bit fiddly even when run manually.   


  [1]: http://superuser.com/a/508470/40354
  [2]: http://Autohotkey.com
  [3]: https://social.technet.microsoft.com/Forums/windows/en-US/0462579d-780a-460a-befd-90f755e902aa/how-to-schedule-a-task-on-resume-from-sleep?forum=itprovistaapps