While messing around, I found it is possible to get OOB with the cube jump in the extra challenges (I assume it works for all). Here is a video of it:

I think it may be possible to skip massive parts of chapters, since some ceilings do not have collision.

¤¤¤I managed to get the cube past the barrier, meaning the whole sector can be skipped! I simply did a cube jump on the left wall [when you enter] and found the cube on the other side. It is likely, however, this would not save much time, if any.

Ooo, interesting. Reinstalling now.

I actually looked at other chambers and you can get OOB in all of them with cubes.

Yeah, trying to see if I can abuse the oob in 26 right now. The rest of the level goes up so it's hard to see what would happen

Do you press spacebar or are you just going against the cube to get trough the ceiling ? Would love to break the game but sadly i cant get it... even with understanding kickflips