Try the "listen-address=" directive:
pi@noads:~ $ man dnsmasq
[..]
-a, --listen-address=<ipaddr>
Listen on the given IP address(es). Both --interface and --lis‐
ten-address options may be given, in which case the set of both
interfaces and addresses is used. Note that if no --interface
option is given, but --listen-address is, dnsmasq will not auto‐
matically listen on the loopback interface. To achieve this, its
IP address, 127.0.0.1, must be explicitly given as a --listen-
address option.
[..]
You can put that directive in a new dnsmasq config file that will be read by pihole-FTL:
sudo nano /etc/dnsmasq.d/99-my-settings.conf