USB to ethernet adapter maybe? you can check if its really wifi by putting it in a metal box to block wifi.

maybe im overthinking it, there might be an easier way.

android emulators (Ldplayer and all) have fake wifi networks maybe try on that

Burner phone?

If you control the device and can root it, you can definitely fake the connected wifi SSID, the list of available ones, whether you are in fact using Wi-Fi etc with Xposed but it'll probably take research into the current landscape that I'm no longer familiar with. There is no perfect software method on unrooted Android for fake GPS, depending on how motivated the app dev was at detecting it.

I've got one of those hardware GPS spoofers that attaches to the handset, basically jams GPS and impersonates the satellites. Works well. I don't know of a comparable piece of hardware that would both jam wifi for a handset and present a fake SSID unfortunately.

If you can leave the handset in one place you could also remote into it, software like DroidVNC-NG can let you access it from another handset.

Faraday bag?

feels to me like FuckyWucky's got the right idea. it would seem to call for a modified wifi driver that can report seeing the SSIDs you tell it, but then you've got the whole problem of knowing what SSIDs are near where you are supposed to be.