Hey Pipesearch,
There is a nice post about this in the knowledgebase (not easy to find, I know...). The post basically says - and I agree - you should not make motivate your recipients to forward an email because, as you mentioned already, the email will most likely break.
You can create a simple mailto-link and implement this as CTA (Check out Parcel’s generator to do this), which does not include any formatting (which can not break, though).
If you put more resources into it you also can create, as mentionend in the post, a landing page where your recipients can type in the “to be forwarded” email address. From there, you can trigger a campaing in CIO.
Hope that helps,
Felix