Fetch request from google mobile robot does not set is_mobile() to TRUE

[eluser]tomyt[/eluser]
I'm using this tool test how Google indexes the mobile version of my site.

However, regardless of which mobile version I choose (Mobile: cHTML, XHTML/WML, or Smartphone) it always returns the desktop version of the site.

I know settings can be tweaked in the user-agents config file, but I'm looking for guidance as to how. This is important because it's against google's policies to server a different version of the page to google than your regular users. And if they are both using a cellphone, this is something I'm currently doing.

Is there a string I can add to the user agent arrays to detect google mobile bot? And more importantly, where should I include it? Since the order of the array also matters.

Thanks a ton for your help.