Hello and welcome to our forum! If your form is bound directly to the database then you have to actually have that column in the database for it to show in the data source and give you a column to bind to. This means you may need to create this phantom column in the DB that is only used client side.
In terms of your submit, I think you will have to write code to submit only the checked rows though there may be a way to do it when creating the original DB submit data connection parameters such that it filters there. I'm not sure about this. To try it you would go to Tools Data connections and then try to modify your Main data connection to adjust parameters in there.
Shiraz Cupala / Microsoft InfoPath MVPQdabra® Software / Streamline data gathering to turn process into knowledge