In the process of improving my old run, and I came across a way to put Sonic in the wall of Labyrinth 1, with (so far) no practical application.
Zipping to the left runs him into a switch, crushing him. You can also fall below the floor and into a long pit. Zipping to the right is demonstrated here, but tests in debug mode show that the spikes to my right aren't zippable, and the wall to the right of that is only to a point, then halts progress.
It's also possible to glitch into the area below those spikes. This leads to either being stuck, ejected into the normal area, or falling on the ceiling spikes and dying.
It's also possible to jump up into the upside-down T shaped piece of land near the beginning of the underwater area, and zip right from there, but this is pretty much the same as zipping right from the initial position.
Bummer. If anyone has any ideas though, that'd be great.
GMV = here.