How can I use sprite layers in a 3d world?

basically I want 2 or more characters in a 3d world represented by 2 multilayer sprites. I set each layer order in each character , so I have a level 0,1,2...X for each of the characters. I set the respect to the default layer.

they show up fine, but when one is behind the other (his z coordinate is more than the other's) since the sprite layers are respect to the same layer (default) they clip eachother.

how can I solve this problem? since I'm in a 3d world it could even happen that one come in front of the other,so I can't simply refer them to 2 different layer and order them...it should be something dynamic,that puts in front one or the other based on the z coordinates.

Any help will be apreciated.