Hi Marko,
Thanks for reaching out. I will try to help with this question.
As you mentioned, this is not something included with the plugin. I am not aware of any easy way to do this programatically.
You might check out the WP All Import Plugin. This will allow you to import data into your site from a CSV file. The Tickets plugin creates a custom post type for RSVPs. If you are moving data from one site to another, you can also use the default WordPress import/export tool and choose the RSVP post type.
Hope this helps! Please let me know if you have any other questions.
Thanks,
Sky