In the Submit Options for your form, you can choose to submit via rules. One rule would be to submit the form using the data connection you want to submit with. But another action could set a field's value.
So, for example, you could have True / False field in the data source (doesn't have to show on the form) called Submitted. The default value could be false. The rules in the Submit Options would be to 1. Set the Submitted field to true and 2. Submit the form.