Returning visitors who filled out form, but didn't pay, have to fill out form again with differ

Sometimes a person will fill out the form to pay for a membership for my site, but then decide not to go all the way through with the payment. Then, they'll change their minds, and come back. However, on the Registration Page they fill out the form again, but they have to do it with a different email/username as before.

My question is, can I make it to where these people don't have to fill the form out again with different information in order to get back to the payment option?