Here's a viable work around. When you promote the report to Production, determine the Document Creation Date.
Then use this formula to show Certified or Not Certified.
=If(FormatDate(DocumentCreationDate();"M/dd/yy")="6/14/16";"Certified";"Not Certified")
NOTE: Replace my "6/14/16" with your WebI Document's Production Date.
When a user saves a copy, I'm assuming it will get a new Creation Date and start showing Not Certified.
Note: The date format may need to be "M/d/yy" so it uses single digits with no leading 0.