Using NWC, I will distribute a form where the form URL will include a parameter that corresponds to a form control (using getQueryStringParameter).  The URL parameter will be unique to each recipient.  I do not want recipients to see the form control in the form, but when the form is submitted, I want the value of that form control (provided by a parameter using getQueryStringParameter) to be available.

But if the form control is hidden using any standard technique (the field is not visible, there is a rule that hides the form control or the form control is in a hidden group), then the value is not available.

The best I could do (i.e., kludge) is to give the form control label generic text (like "Thanks for filling out this form") and set its styling so that the field itself blends into the background of the form.

Is there another way to do this, such as using custom CSS?  I don't know of any way to apply custom CSS to a NWC form and this capability does not appear to exist:  https://community.nintex.com/t5/Nintex-Workflow-Cloud/Custom-CSS-in-Nintex-cloud-form/m-p/113912

Is there some other means to achieve this goal?