With thanks to Louise Kursmark, here is a sample of a paragraph to include on your "work order" or "authorization to print" forms that will give you permission to fictionalize your clients resume and use it for resume contests and submissions to books. It's an "opt-out" form, because if client's DO NOT wish to give you permission to use their resume, they must take action to do so.
PUBLISHING AUTHORIZATION
I give permission for the content of my resume to be published in articles, columns, books, and industry-related publications or for use in resume writing contests, at the discretion of RESUME WRITER'S NAME, and with the understanding that ALL IDENTIFYING INFORMATION (name, address, name of employer, and so forth) WILL BE FICTIONALIZED to protect my confidentiality. If I do NOT give this authorization, I have "x'ed out" this paragraph.