Bean Shell Form Binder allows you to dictate on how Form Data should be loaded and stored.
Sample Script:
Sample Load Binder that will populate field with id "description" with the value "hello world". 
import org.joget.apps.form.model.*;
FormRowSet f = new FormRowSet();
FormRow r1 = new FormRow();
r1.put("description", "hello world");
f.add(r1);
return f;