I'm going to make the assumption that your "client side code" contains a variable with a unique value that would be passed to SiteCatalyst or otherwise 'notify' that the SiteCatalyst would fire.
// logic to check if my variable does not equal some value
where b.myvar is a unique variable in your data layer that when populated with a specific value means that it's 'ok' for the SiteCatalyst tag to fire. (b is the short-hand notation for the extension's locally-scoped copy of utag.data)
FYI, this is the simplest execution of this method. You may have to write additional logic if the specific variable/value you are evaluating in the "if" statement is not available or populated at the time that the extension executes.