For now you could use an on text event, there's a little bit more code here than what you need, but this lets you run certain urls that mIRC won't handle.

Code:
alias urlunderline { $iif($1 == on,.en,.dis) $+ able #url }

#url on
on *:input:*:{
  if (!$istok(/ $readini($mircini,text,commandchar),$left($1,1),32)) && (!$ctrlenter) {
    var %input = $1-
    .echo -q $regsub(%input,/((?:ftp:\/\/|https?:\/\/|www2?\.)[^<>\.\s]+(?:\.[^<>\.\s]+)+(?:\/[^<>\.\s]+)*)/g,\1,%input)
    .echo -q $regsub(%input,/(irc:\/\/[^<>\.\s]+(?:\.[^/<>\.\s]+)+(?:\/[^/<>\.\s]*)?\/?(?![^\s\x2c\.]))/g,\1,%input)
    .echo -q $regsub(%input,/(aim:goim\?screenname=[^\s&]+(?:&message=[^\s&=]+)?)/g,\1,%input)
    say %input
    halt
  }
}
on ^*:text:*:*:{
  var %text = $1-
  .echo -q $regsub(%text,/((?:ftp:\/\/|https?:\/\/|www2?\.)[^<>\.\s]+(?:\.[^<>\.\s]+)+(?:\/[^<>\.\s]+)*)/g,\1,%text)
  .echo -q $regsub(%text,/(irc:\/\/[^<>\.\s]+(?:\.[^/<>\.\s]+)+(?:\/[^/<>\.\s]*)?\/?(?![^\s\x2c\.]))/g,\1,%text)
  .echo -q $regsub(%text,/(aim:goim\?screenname=[^\s&]+(?:&message=[^\s&=]+)?)/g,\1,%text)
  echo -bcflirt $iif($chan,$chan,$iif($query($nick),$nick,$target)) $+(,$cnick($nick).color,<,$iif($gettok($readini($mircini,options,n2),30,44),$left($nick($chan,$nick).pnick,1)),$nick,>) %text
  haltdef
}
on $^*:hotlink:/aim:goim\?screenname=[^\s&]+(?:&message=[^\s&=]+)?|irc:\/\/[^<>\.\s]+(?:\.[^/<>\.\s]+)+(?:\/[^/<>\.\s]*)?\/?(?![^\s\x2c\.])/:*:{ return }
on *:hotlink:*:*:{
  if ($regex(aim,$1,/(aim:goim\?screenname=[^\s&]+(?:&message=[^\s&=]+)?)/)) { run $regml(aim,1) }
  elseif ($regex(irc,$1,/(irc:\/\/[^<>\.\s]+(?:\.[^/<>\.\s]+)+(?:\/[^/<>\.\s]*)?\/?(?![^\s\x2c\.]))/)) { run $regml(irc,1) }
}
#url end

menu menubar {
  $iif($group(#url).status == on,$style(1)) Url underlining: urlunderline $iif($group(#url).status == on,off,on)
}