Hmmm... I hope I understand you right.

each object should have a collisionshape. I think in most cases a rectangle or circle is enough.

When you test your player if he collides with an object, test his feet area only to see if his feet are colliding with the object. If the feet are above the collision shape of the tested object, draw the object in front of the player. If the players feet are below, the player is in front of the object.

So basically, the collisionshape of each object is half the height of the objects bitmap itself when view from an 45¬? angle.

Hope you understand what I mean. Don't test the whole player, just his lower part, depending on your view. A screenshot would be nice to help you detailed....

Greetings,
Dirk