there are ways to make platforms as walls and or holes & change their position on levels using script.
so you may be able to use a wall as a z boundary for a certain portion of the level , and shift it as needed
example, this hospital level's true z boundary of the level is this portion where the doctor appears:
whlie the rest of the level features platforms to simulate changes in depth:
also
depending on what you wan to do, another options is to use entities with platform attributes to act as walls or boundaries, doors and they have the advantage of being able to move using "jumpframe" or scripts to move about