I found a bug where using a thin yellow clip does not fully block a player from walking along a ledge.
You can recreate this bug by doing the following.
1. Get as close to the clip as possible
2. Stand still
3. Jump once
Note: There is no need to do anything other then get next to it and press spacebar. No shooting, no strafing, no crouching, you don't even need to move. Just move next to it and tap spacebar once.
This doesn't work 100% of the time so you may need to try a few times.
Conclusion: This is a bug with the clip being too thin, it can be prevented by making the clip thicker like the one on the north wall of the room. It is not flyhack.
(The map used for this example is Kirby-Gema-2.cgz rev 83)
The bottom two yellow clips are thin
You can see that they don't fully cover the ledge
The spot I use in demo to get onto ledge
P.S. You can even edge jump off the ledge behind the clip.
Another example found on Gema_Ice
The jump is higher for this one so you'll need to shoot downwards to gain height.
1. Move up as close as possible to the side
2. Turn so that your back is against the wall
4. Shoot downwards
The reason for having your back against the wall is to prevent gun recoil from moving you away from the wall.
Demo (/setmr 13)