How’s the wifi in the garage (guessing also bad)?
If it’s possible to have more than 1 zwave network with zwavejs (this I do not know), you could use this setup: Make a Z-wave to WiFi bridge with esphome stream server and Zooz ZAC93 GPIO
and have the garage be its own zwave network and backhaul over wifi. Looks like this project can be usb-powered.