sudo apt-get install xdotool wmctrl

#!/bin/bash
if [ "x$*" != "x" ]; then
  /usr/bin/gnome-terminal "$@"
else
  pgrep -u "$user" gnome-terminal | grep -qv "$$"
  if [ "$?" == "0" ]; then
    wid=`xdotool search --class "gnome-terminal" | head -1`
    xdotool windowfocus $wid
    xdotool key ctrl+shift+t
    wmctrl -i -a $wid
  else
    /usr/bin/gnome-terminal
  fi 
fi