As a tribute to the former Back to the Future ride that the Simpsons Ride's spot now occupies Doc Brown makes a cameo in the pre-show video.
Krusty the Clown:
Hey, hey! Good news, the line's almost over! Only 45 more minutes! Just kidding, I don't know how long it is.
When the Simpson family are sitting in their living room, the floor, walls, and ceiling fly out into space. Off the the very right of the screen, a pink wall can be seen floating away. It then completely vanishes in mid air. (It is best visible if you're sitting on the right top level of the theater.)