$HTTP["host"] =~ "domain1.tld" {
        server.document-root = "/var/www-domain1.tld"
}
$HTTP["host"] =~ "x.domain1.tld" {
        server.document-root = "/var/www-x.domain1.tld"
}

$HTTP["host"] =~ "x.domain2.tld" {
        server.document-root = "/var/www-x.domain2.tld"
}