I get it. The default unsubscribe page is lame and boring. You want to add captcha and a little branding to it.
You do have an option. You can build a custom unsubscribe form and page.
In Interspire Email Marketer you can visit the Forms menu and create a new form. That form has a lot of options just like a subscribe form.
Then you can take that form and embed it on any web page and then in your email campaign where you would normally put the unsubscribe link you instead can link to the new page with the unsubscribe form.
There you go. Very simple.