Yeah, without the social module that would be hard to do. Sure is interesting as to where that lead came from with that source. It shows in both Marketo and Salesforce, or just Salesforce? We are in a similar situation in that we have lots of leads with very little information besides email addresses. We place those in what we call our Basics General Nurture program where over a series of emails we prompt them to provide us with additional information. One was high-level message about who uses the products in our industry, one was a link to signup for our company email newsletter, one was a drawing for merchandise, one was to vote in a poll and the last ask if they had a request for morei nformation.
The overall intent was to gather additional information about those contacts so we could place them in the proper nurture streams. About a third of those we engaged with responded with additional information. We deleted the remainder.
Hope this helps.