First install an instance the normal way.

Then grab the image from [here](https://cloud-images.ubuntu.com/wsl/jammy/current/) -- the file is called `ubuntu-jammy-wsl-amd64-wsl.rootfs.tar.gz`

Then
```ps
wsl --import <Distribution Name> <Installation Folder> <Ubuntu WSL2 Image Tarball path>
```
e.g.
```ps
wsl --import ubuntu2204c C:\Users\mrflibble\wsl\ubuntu2204c ubuntu-jammy-wsl-amd64-wsl.rootfs.tar.gz
```
This also works fine in cmd or cygwin, though with cygwin you need to ensure the paths are Windows paths (use `cygpath -w /nix/path`)