Not sure about Sitecore CMS but we've successfully used iframes inside our WordPress CMS.
Set up all assets (form, landing page, follow-up page) on a blank Marketo landing page and just include an iframe on your CMS page to the MKTO landing page with progressive profiling. Control page sizing either on your Marketo page or call it on on the iframe so users can't scroll. Be sure to test it on multiple browsers.
An alternative to using an iframe would to use a dummy form. You would set up that form on a blank Marketo page, then grab the source code for the form and paste it directly onto your CMS page. For this method, however, I'm not sure you can get progressive profiling to work (never tried).