1. create a mission for the multiplayer
2. create two playable unit slots
3. place an object (f.e. a small container) near the units
4. in the init line of the small container insert following code: this addaction ["Open Virtual Garage", {["Open",true] spawn BIS_fnc_garage}]
5. save and preview the mission (invide your buddy to join the mission)
6. now go to the container and play around with the Virtual Garage