The other option is to set root's DISPLAY environment variable to the user's session. Something like:
$root ~> export DISPLAY=:0.0
$root ~> ./guiprogram
You may need to do "xhost +127.0.0.1" which allows local X connections. Another option is to open an xterm on the local display, using something like "xterm -display :0.0", and launch commands from there.
Hopefully that helps.