How do I change the order in which objects are rendered?
 

I am attempting to use Turtle for Maya to render environment maps for in-game use, but I am having problems with objects rendering in the wrong order, which causes decals (such as painted lines and skidmarks on a race track) to appear incorrectly. The materials are named in such a way (with prefixes such as L1_, L2_ etc) that it forces the game engine to render them in a specific order.

Is there any way to force Maya to render objects or materials in a specific order, as the game engine does?

It seems like my rendering order problem has something to do with a few very large objects in the scene (deleting them fixes the problem with the render). Is the accuracy of Maya's z-buffer related to the size of the largest object in the scene?