Lead Conversion to existing contact

When we get a new lead generated from our webform, we would like to link that "lead" to an existing contact/account. Sometimes current customers fill out our webform and currently, we would need to convert that lead. Then search for both accounts in the contacts section and merge them. 

When we click "convert" on a lead we would like the ability to link that to any existing contact record right from the conversion box. Not sure how much development would go into a suggested matching record. When you click convert, ZD will search all fields with data and find/suggest any matching records or give us the option to search for an existing record.