Any applicant is eligible for consideration under this quota subject to the rules of the University in force. (Sponsorship Certificates / Relationship Certificates are not required for applying under Non-Resident Indians (NRI) quota).
I sugeest you take all your certificates for walk in to the interview. No special certificates are needed.
CUSAT CAT Prospectus 2013 Page 88 - http://bitly.com/108H9jm