Oh, I like it!
The entire OS runs from a Corsair MP600 MINI in a DockCase USB-C NVMe enclosure. No internal drive modification needed. When I want to game, I unplug the drive and reboot into my main Windows install, and game normally on the 4080. When I want to do LLM stuff, I plug the drive back in, reboot into NixOS, and both GPUs are available.
From I Put a Datacenter GPU in My Gaming PC for £200 article.