If you don't want to see the raw output of the trace replies, you could make a raw event for each trace numeric and haltdef it.

raw 200:*:haltdef
raw 201:*:haltdef
raw 202:*:haltdef

etc.

If you want to trace each user that joins the channel, you could do this...

Code:

on *:JOIN:#: {
  if (($nick == $me) || ($eval($+(%,didtrace.,$nick),2))) return
  set -eu60 $+(%,didtrace.,$nick) $true
  !trace $nick
}

...and then catch the reply with your raw 205 event and do with it what you want from there.

You could replace the # with your channel name(s) if you only want it to work on a certain channel(s).

on *:JOIN:#chan1,#chan2,#chan3: {