Geolocation banning of signup form

I'm using the mod_maxminddb apache module to block access from all countries outside the US, but I don't want to be quite that drastic.  I just want to prevent users from outside the US from joining, while still allowing them to view content.

Current .htaccess looks like this:

MaxMindDBEnable On
MaxMindDBFile COUNTRY_DB /usr/share/GeoIP/GeoLite2-Country.mmdb
MaxMindDBEnv MM_COUNTRY_CODE COUNTRY_DB/country/iso_code
SetEnvIf MM_COUNTRY_CODE ^(AU|US) AllowCountry
Deny from all
Allow from env=AllowCountry

I'd block AU, but there's some guys I know down there, that seem like decent folks.  I know how to do this in Dolphin's join.php file, but since the sign up form in una seems to be a dynamically generated page, I'm unsure how to do it.  What I need to do, is block the join page, and ONLY the join page, using the environment variable 'AllowCountry'

I'd probably figure this out all by myself in a few years, but I'n in a bit of a hurry, so any brilliant advice would be appreciated.