This would be possible with a custom Pipe that inherits from Telerik.Sitefinity.Publishing.Pipes.SyndicationPipe and you should override uildSyndicationItems(IList<IDictionary<string, object>> internalFormat). One of the parameters of this method is internalFormat from where you can get data for the content item and decide whether to rend it or not.
Currently there is an issue with the custom pipes and actually you will not be able to create a custom pipe. We are working on the issue and we logged a task for it.
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