I'm using the 'geoip' module that comes with PowerDNS (for a few years), combined with the RBLDNS lists from
http://countries.nerd.dk/. It works rather well, and can be adjusted to accommodate custom/existing geo-specific regions, not just countries, but ISP CIDR's.
I'd go with the following syntax:
/operserv DNS ADDZONE zone.name
/operserv DNS DELZONE zone.name
Example:
/operserv DNS ADDZONE us.network.net
And change the POOL and DEPOOL to:
/operserv DNS POOL server.name zone.name
/operserv DNS DEPOOL server.name zone.name
Example:
/operserv DNS POOL server.network.net us.network.net