Is there a way to automatically insert the GeoIP region of source IP of all requests into a custom header in WAF configuration ?

Technically the terraform configuration could look like this :

resource "aws_wafv2_web_acl" "my_web_acl" {
  default_action {
    allow {
      custom_request_handling {
        insert_header {
            name  = "X-Country-Code"
            value = "#{geoip:country:iso_code}" <<<< ????
          }
      }
    }
  }
}

But I don't think there is a way to put anything else than a static value in the value field.

Is there any way to do this ? (in WAF or ALB configuration maybe ?)