Could you add hostname option to in_tail.rb ?

Configuration : 
<source>
  type tail
  format /^(?<remote>[^ ]*) (?<host>[^ ]*) (?<user>[^ ]*) \[(?<time>[^\]]*)\] "(?<method>\S+)(?: +(?<path>[^ ]*) +\S*)?" (?<code>[^ ]*) (?<size>[^ ]*)(?: "(?<referer>[^\"]*)" "(?<agent>[^\"]*)" "(?<forward>[^\"]*)" (?<response_time>[^ ]*))?$/
  path /usr/local/nginx/logs/access.log
  pos_file /var/log/td-agent/access.log.pos
  time_format %d/%b/%Y:%H:%M:%S %z
  tag hostname.in.tail
  hostname_command hostname
</source>

Result :

2012-11-27T00:00:43+09:00       hostname.in.tail  {"hostname":"myhost","remote":"172.28.32.249","host":"-","user":"-","method":"GET","path":"/monitor","code":"200","size":"15","referer":"-","agent":"-","forward":"-","response_time":"0.003"}