i would add a scene in ANH with Sebulba begging for credits in front of the cantina. and as Luke and the crew enter the cantina, 3PO notices him and utters "Oh my". and to further ruin the movie, have Sebulba talking to the Stormtroopers outside of the cantina while the droids look on.
for the ESB, when Luke stops his training with Yoda to save his friends on Cloud City, when the ghost of Kenobi and Yoda both fail to keep Luke there, a ghost of Mace appears and says "This party's over, that boy was our last hope."
ROTJ, just replace the perfectly acceptable ghost of the old Anakin with the younger one... oh, wait.