Two questions in one day--is that permitted? :-)
Is there a way to include an opt-in link to an email sent out via Forward To A Friend? Or is it a matter of including, in the original email, a link to a subscribe form on a web site?
At this stage you can't specify content that will only appear in the forwarded version, so your best bet is to include a call to action to subscribe at the top of the email somewhere. Maybe something along the lines of:
"Did a friend pass this newsletter on to you? Click here to subscribe and get your own copy each month"
Haha, brilliant stig. If you want a teaser, this was certainly one of the aspects we'd be considering to get the ball rolling in this area.