I think the following code should be producing a list of channels that a selected nick is in, but that I'm not. Sort of the opposite of the $comchan identifier. However, my testing shows that it's still coming up with all of the channels, not just the one's that are different (or none if all are the same)
Code:
 raw 319:*:{
  did -v Channel_Control 1019,1020
  var %a = 1, %b = $numtok($3-,32)
  while %a <= %b {
    var %temp.chan = $gettok($3-,%a,32)
    if $me !ison %temp.chan {
      did -a Channel_Control 1020 %temp.chan
    }
    inc %a
  }
  ;didtok Channel_Control 1020 32 $3-
  did -rva Channel_Control 1021 $did(Channel_Control,1020).lines
  halt
}