Change OWA 2010 message composition to default to plain text

Currently OWA 2010 defaults to HTML format when users compose a new message. I would like to change that default to plain text, but still allow them to change to HTML should they require it for message content needs.

Is there a way to do this at the server level? I do not want to force "Light" mode or make changes to individual mailboxes.

Thanks,

Christiaan

Christiaan Zaluzec