I don’t really know how Typeform responses are being created in ERPNext … manually? I assume that you are using ERPNext API to do that … As Typeform seems to have an static webhook data structure, have you created a specific API method that receives Typeform data and insert records in your doctype? If you are doing it, you can insert doc in lead doctype too …
Maybe I missunderstood your requirement.
To create leads automatically:
Create a server script
Type: Doctype Event
Reference Doctype: Typeform responses