You might use dynamic content to show a link to the landing page on your thank you page. This should work with anonymous segments:
http://community.marketo.com/MarketoTutorial?id=kA250000000Kz0hCAC
If you're concerned about losing information on your leads, consider sending your content offers via email rather than direct download links. This will help with email deliverability, verify accurate information, and make it a bit more difficult to share your content via Twitter.