[syslog-ng] Selective application of keep-hostname()?

I have a use case where I need to selectively apply keep-hostname(yes) to messages from certain source IPs, while defaulting to keep-hostname(no) for the rest of my sources. I know I can apply this option on a per-source basis, but in this case I want to be able to selectively apply this option based on the source IP of the message. I'm trying to avoid having to set up an alternate port if I can. Thanks Steve