👷♀️ Under construction... 🚜
TL;DR: Leave the first space on your monitor empty forever and just have a second space. The empty first space on the monitor will merge with the first space on the laptop when you unplug the monitor. The 2nd through Nth spaces on the external monitor will move onto the laptop with thier windows. When you plug the monitor back in, the 2nd through Nth spaces will move back to the monitor as expected.