I have a similar request really: all my desktop computers ae rack mounted, so, inside a metal box known as a server rack, and I need Bluetooth. If the cable run is short, for example in my case which the signal just need to be brought out of the metal box, you can use coax if your wireless hardware allows it. Usually it means a stretch of SMA cable. There are also cables that has a magnetic antenna stand on one end.
If the cable is a bit too long, you can use a Raspberry Pi 3 or above as the wireless to Ethernet adapter. Raspberry Pi 3 needs some form of 5V local power which can be derived from a solar panel and local batteries. Pi 3+ and above allows PoE which allows power be sent over to the Pi using the Ethernet cable. Alternatively there are also a lot of Mediatek MT7688 based modules out there. That is a wireless router chipset ad Mediatek released all of its documentations and drivers, allowing fantastic LEDE support.
On the topic regarding hard cabling t your neighbor's, fibre optics can be treated differently than Ethernet cables in building codes as those are often constructed entirely out of non-metallic materials, thus non-conductive. (Example: in the building code in Shanghai, Ethernet cables are not allowed to share conduit with mains wiring, but fibre optics can.) If your neighbor and the local regulation allows it, you can run a pair multimode fiber between the premises.