I can only think of a way that would require some javascript on the landingpage.
Hidden field on the form.
Trigger Campaign sets a value in that field after a form is first submitted.
Then some javascript checks to see if there is a value in the field.
If there is redirect the papge or display a different message.
If you were planning to roll this out to all landing pages you might neeed to create a lot of custom fields for the check.