How do I handle Isometric collision detection?

I would like to make an isometric run-jump style platformer. The player should be able to jump on top of platforms above the floor, hit the side of objects etc.

I'll be using a 2D game engine so I wouldn't like to emulate full 3D collision for dimensions I'm not using.

I'm thinking objects in the game should be placed using: X, Y, width, height, and Z for depth.

Using those values, how should I detect collisions?