Another way to do this would be to hack the code decoding the debugmsg settings to recognize +relay and set +tid at the same time, so that '+relay'=='+relay,+tid'=='-tid,+relay' != '+relay,-tid'. But the last two may be confusing.
what about a +notid channel ? I know it's against the semantics of the channel, but it's close to what you're looking for... A+