While coding Snakeman's Search Snake, I've discovered a way to make the helper (or the char) to bind on the walls.
For Mugen 1.0:
[State 0, PosAdd]
type = PosAdd
trigger1 = facing = 1
x =GameWidth-ScreenPos X
ignorehitpause = 1
[State 0, PosAdd]
type = PosSet
trigger1 = facing = -1
x =-GameWidth/2
ignorehitpause = 1
For Winmugen:
[State 0, PosAdd]
type = PosAdd
trigger1 = facing = 1
x =320-ScreenPos X
ignorehitpause = 1
[State 0, PosAdd]
type = PosSet
trigger1 = facing = -1
x =-160
ignorehitpause = 1
Additionally, if you need to bind the helper to the top of the screen(I don't remember who made that, maybe it was Hero):
[State 0, PosSet]
type = PosAdd
trigger1 = 1
y = 0-ScreenPos Y
ignorehitpause = 1
persistent = 1