I just looked at the help/faq section in Wells Fargo SurePay under my account, and I think I found the answer to my question. I'll copy and paste what I found under the "How do I receive money?" tab:
When someone sends you money, you will be notified at the email address the sender used to send you money. If this email address has not yet been registered, you can update your existing contact information, or register the new email address. Your mobile number will not be eligible to receive transfers until it is registered with WF SurePay or clearXchange.
clearXchange is a network of banks that allows customers of other financial institutions to receive money with WF SurePay.
Customers of member banks can use their bank’s online banking to register, and customers of non-member banks can go to clearXchange to register. Current member banks in the clearXchange network are: Wells Fargo, Bank of America, Capital One, Chase, US Bank, FirstBank, Frost Bank, and TD Bank
So to me it seems as if it isn't required that you do the actual "signing up" if you are a member of the current cXc member banks; as long as you have your email and phone registered with your associated bank who is in the "member bank" list.