How to force Outlook 2007 Calendar invites to display as Plain Text?

1.  User receives a meeting request in Outlook 2007.

2. User opens the meeting request.

3. User clicks on the calender invite to view contents.

4. Instead of the calendar invite opening in an HTML format, we want it to open in Plain Text format.

Anyone with an idea about how to configure outlook calendar invite to open in Plain text format?

I know this can be done either through Outlook admin template settings or the registry setting via GPO. I just do not know the correct registry setting or admin template setting. I've googled around for a very long time for this info.

Thanks,

TeeDarling77