A workaround is to continue using the router DHCP, but limit the IP range to a single IP, that of the Pi. The Pi will get it's address from the router.
Then use the Pi-Hole DHCP and set its IP range to a non-overlapping range from the router DHCP.
Example - Pi is at IP 123. Router DHCP set on range xxx.xxx.x.123-123. Pi-Hole DHCP set to range 50-100.