How does one set "-i" for postmaster on RHEL7 PostgreSQL?

Hopefully I am not missing something obvious, but I can't seem to resolve how to provide the necessary "-i" to postmaster to get it to listen for non-local network connections.

/usr/lib/systemd/system/postgresql.service has

ExecStart=/usr/bin/pg_ctl start -D ${PGDATA} -s -o "-p ${PGPORT}" -w -t 30

back in the good ole days of RHEL6, getting PGOPTS="-i" in proper /etc/sysconfig file would do the trick.

Thanks!