During install of the custom image, `pi flasher` allowed me to configure things like the hostname, ssid, my ssh key, my user account. This sets up a script that runs when the pi reboots for the first time after install.
1. Mount the pi's `/boot` volume (it should be in your file manager somewhere)
1. Edit the `initial-boot.sh` (or similar named script)
1. Add `ssh-keygen -A` somewhere in the file
1. Save and close the file
1. Safely unmount the pi's `/boot`
1. Done! The ssh server is now functional
_Alternatively, you can wait for the system to boot with a keyboard and monitor connected and:_