Update multiple Piholes on change

What would you like to be added: the current options allow externalDNS to update a single Pi-hole. I'd like to be able to point it at multiple Pi-holes.

Why is this needed: I run a backup Pi-hole that needs the same configuration as the primary. I have some records managed by externalDNS that currently I can only update by running a second externalDNS deployment (I believe), and I would much rather only have a single deployment to manage.