This is an interesting idea and I agree this could be useful. Will have to see what kind of traction it gets in the Community to see if it might be something TT adds to their very long list of ideas to implement.
As an immediate work around if you go ahead and create a New Contacts patrol and add in the people who’s contact information you have gotten but just uncheck the box to send a registration link to them. They would not be registered with TT accounts but you could then select them as a group to send e-mails.
If you all ready have a spreadsheet of these people you could use the importer, not sure if the registration e-mail is automatically sent with the import method, I did pose that question in that thread: