Here's another solution for you.

http://www.digitalcarversguild.com/plugin.php?ProductId=13

Shaders Plus has a function called Procedural Lock that works great for your problem. Plus is it has a few other goodies tucked away inside. I used it several times in a shader experiment project I was working on a while back.

Headwax's suggestion of Baker will also work. I've used that plugin a few times as well.