RRC in MGM could really use one too, and it doesn't.
Just a note, I've found that as you approach the front of the line, if you hold up one finger you will often be pulled and seated as a fill-in rider if it is easy for you to hop out of the queue. I've done this on RRC, KS, Kali, Dinosaur, Space, BTMRR, and Splash.
This is NOT a major time saving technique and is definitely not something that it's worth breaking up a group over; you will never be moved from a couple hundred people back to the front of the line. Total time saved is approx 2-5 minutes depending on the ride with the average being in the 2-3 minute area; Space is the ONLY one that I have saved any appreciable time and they were specifically requesting single riders. But it's a nice way to shave off waiting for a train or two if there's others waiting outside for you.