I have found this to be simpler that the above. Simply edit the /etc/hosts file on the Pi-hole and put the IP and FQDN in.
The line in the man page for dsnmasq that gives a clue:
It loads the contents of /etc/hosts so that local hostnames which do not appear in the global DNS can be resolved
I now have a wildcard SSL certificate and multiple machines on my LAN happily serving over HTTPS. I do have to update the certificate onto each machine - I may look at a reverse proxy (or maybe not!)