I think what you are looking for is called Multi-Pass Rendering and there is a Tutorial about it on the ForgeWiki!
I can't say if the code provided there will work for 1.5 since i'm pretty new to Java but at least it's a start
http://www.minecraftforge.net/wiki/Multiple_Pass_Render_Blocks
From what i know the SecretRoomsMod has some sort of MPR going on and it get's currently ported to 1.5 so with the tutorial on the wiki and the source insight from Github you're on the right way.
https://github.com/AbrarSyed/SecretRoomsMod-forge
Hope it helps