I know that this thread is ancient ... but ... is there still a way to preconfigure WiFi?
There never has been a way to preconfigure it (LE has never packaged os_config.json). I'd suggest you force the SSH daemon to start by adding "ssh" to boot params in cmdline.txt and then connecting an Ethernet cable. As you have not configured an IP on the RPi it will auto-configure itself with a 169.254.x.x/16 address. In the absence of DHCP the device you need to connect from should also self-configure itself in the same range (which is a large range) and you can run arp -a or perhaps ping the broadcast address (the .255 address of the local subnet) to discover the other device's IP address; and then connect over SSH. Once connected over SSH you can run connmanctl > agent on > scan wifi > connect <name-of-service> to configure the network connection, and use kodi-remote to navigate around the screen. If you struggle with the remote IP discovery another approach is to have your computer connect to WiFi and then share its connection via Ethernet to the RPi, which results in the RPi using a known IP subnet that requires less guesswork.