Nokia here map data for Android - download on pc and move to phone
I could suggest you to use an emulator like Andy. Using this will help you to use your computer's Ethernet to access Internet.

You can install the app on that emulator and download the map data. Then you can either identify the download area and copy them to your phone. If that's too cumbersome you can rely on apps like titanium backup to restore the data alone.

It would be helpful for you if you use the same Android version on both emulator and phone.