As a phan, I've got some recommendations. These are songs that, in my mind, exemplify the Phish live experience: Maze, Run Like an Antelope, Harry Hood, and Slave to the Traffic Light. Anthems like YEM, Bouncing Around the Room, and Fluffhead usually only turn off new (sober) listeners.
Other songs that could help the cause, based on their stand-alone merits, include Down With Disease, Free, Rock and Roll, Suzy Greenburg, Punch You in the Eye, and Piper.
Finally, have Scott listen to Gettin' Jiggy Wit It or Tubthumping from Hampton Comes Alive. That'll give him a glimpse at Phish's tongue-in-cheek sense of humor, and should open up the discussion a bit. Thanks for doing this, guys.