height of the ground is Z position. Y position is either your front or your back. For example you created an object inside yourself, and you did "+y 1" to move the object, then the object moves right in front of you. When you do "-y 2" it passes behind you.
About your question, for me, it's possible with airbreak into Y position, or a spam with something like /gotopos or similar. If i were an admin for example and if i were to find that map, i would spam this :
/gotopos 1921.842 100.0 15.0
*couldn't find ? ==>
/gotopos 1921.842 200.0 15.0
*again couldn't find ? ==>
/gotopos 1921.842 400.0 15.0
/gotopos 1921.842 600.0 15.0
/gotopos 1921.842 900.0 15.0
[...]
I don't know any other ways than that. If you have a teleporter like that you could give it a shot.