While you could do that in Marketo (somehow) I would probably do it in Salesforce. He's already going to be in there anyway. I would filter a SalesForce...
Just thinking out loud; you could make a smart list in marketo that tracks activities (regarding emails, website, and clicks) if it gets triggered put them in a SF campaign or fill in a custom field and push it to salesforce that you can do reporting off of.
Then on the salesforce side you could say "search for everyone and check to see out of the pool of leads, what ones have been contacted, Converted, and still need to be contacted" I'm guessing you track the stages? If not, that’s something you should setup for sales. Status or Stages
Examples would be...
New Lead, Open Lead, Contacted Lead, Conversed lead, Disqualified Lead, and Lost Lead. (or something)
Here's a good resources to help you with getting that up given it's not already setup