v1.2
Just sideload the app on your watch and you can then long-press the bottom button on your Galaxy Watch 4 to launch Google Wallet (install it from the Play Store if not preloaded).
NOTE: Requires a watch reboot to take effect.
Users who haven't received the update rebranding Google Pay to Google Wallet should stick to version 1.0.
NOTE: Only works on watches shipping without Samsung Pay, i.e. only for watches sold in certain regions. For other users, use GW4Remap instead.