Posting in the Magento forums has been disabled pending the implementation of a new and improved forum solution which should better serve the community.
For new questions please post at magento.stackexchange.com, the community-run support site for the Magento community. We will be providing updates on the new forum solution soon. For questions or concerns please email email@example.com.
I think a pretty simple solution here would be to create an attribute for these types of links and populate that attribute for the products you want. You can also control whether this attribute is visible or not (i.e. on the product page).