Since I use SmartDNS for my TV and FireTVs to access Zattoo in Swiss (I am German) I started using the following settings in DNSmasq (/etc/dnsmasq.conf):
dhcp-host=-MAC-Address-,set:smartdns #TV
dhcp-host=xx:xx:xx:xx:xx:xx,set:smartdns #TV
dhcp-host=xx:xx:xx:xx:xx:xx,set:smartdns #FireTV
dhcp-host=xx:xx:xx:xx:xx:xx,set:smartdns #FireTV
dhcp-host=xx:xx:xx:xx:xx:xx,set:smartdns #FireTVStick
dhcp-range=set:smartdns,192.168.178.50,192.168.178.99,infinite
dhcp-option=tag:smartdns,option:dns-server,54.93.173.153,81.17.17.170
Doing so, all clients above and in IP range 192.168.178.50 to 192.168.178.99 use SmartDNS, the rest is using the defined DNS in pi-hole.
It is not perfect but it it works. To see this is out-of-scope is very sad because you see, it is very easy to implement into DNSmasq.