Basado en :
https://discourse.pi-hole.net/t/secondary-dns-server-for-dhcp/1874/4
sudo nano /etc/dnsmasq.d/02-pihole-dhcp.conf
dhcp-option=6,Pi-holeIP,SecondaryDNSIP
sudo service pihole-FTL restart
ejemplo aplicado : dhcp-option=6,192.168.1.2,8.8.8.8
156.154.70.22 DNS Comodo firewall
156.154.71.22 DNS Comodo firewall
200.28.4.130 DNS Movistar
200.28.4.129 DNS Movistar