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It totally depends on the church that issue the certificate.
In many denominations - especially Baptists and other evangelical congregationalist denominations - the certificate itself is generated by the church secretary. It is not a legal form, even if it can be used as a proxy for a birth certificate in some circumstances. In a Roman Catholic church, or another more hierarchical one, the pastor may have less discretion as to the form of the certificate, but good pastoral care will usually lead him to find another solution.
As a non-official document, pastors can exercise discretion in how it is made out - and if there is a genuine request to help another's feelings, good pastoral care would suggest that a pastor should make a reasonable effort to accomodate the request.
In situations where the godparents' names do not appear on the certificate, the pastor would usually be willing to sign some form of acknowledgement that the parents have selected whomever as a godparent.
The key duty of a godparent, other than shock, horror, renouncing Satan is to vouch for the Christian upbringing of the child. Even if the godparent is not present, if he or she is willing to take the same vow, most pastors would likely honor the request, and signify it some fashion if requested.