Can you not just add an IPv6 entry for it in your hosts file, e.g., ::1? That would work in Linux and seems like a much less nuclear option than disabling ipv6 all together, but admittedly I've never worked with ipv6 networking on Macs.

Last time I played with a Mac they also had the BSD `ipfw` command for kernel packet filtering [1]. Could try something there if it still exists.

[1]: https://www.unix.com/man-page/FreeBSD/8/ipfw/