Something

# domain.com or www.domain.com
$HTTP["host"] =~ "^(www\.)?[^.]+\.[^.]+$" {
		evhost.path-pattern = "/var/www/vhosts/%0/www/"
}

# foo.domain.com
$HTTP["host"] !~ "^(www\.)?[^.]+\.[^.]+$" {
		evhost.path-pattern = "/var/www/vhosts/%0/subdomains/%3/"
}