Submit Button on Final Question Only

Is there a simple way to make the “submit” button show on the final question only?

Here is why… (when we have the “previous” button activated)
– user gets to the last question and the “submit” button appears.
– user does not answer the last question
– user clicks “previous” to go back
(the “submit” button is now showing on all pages)
– user tries to hit “submit”
– user gets an error because the final question has not been answered

The page I need help with: [log in to see the link]