Can I somehow unlock my phone's bootloader or root it?
I have the developer edition of Ghost, so never had this problem with unlocking the bootloader.  Did you try RockMyMoto?  You probably have the camera patch by this time, so this might be the method you need.

If that works, I suggest you flash one of the 7.1.2 ROMs over there at XDA after you get TWRP 3.1.1.  Mine is rocking Xperience right now.  Your phone will thank you :)