[SOLVED] Specify header image per post

I've read over these forums for hours and have not been able to find the solution. I found JuggleDads solution for setting the header image based on category or page (thanks JD), but it does not work on posts, at least not for me.
I am using mod rewrite, so even though my post id number is 641 the url reads as the name of the post. Using the url in my css inserts has been working for the categories.
I've been making my changes in the css inserts section for the categories, and again they work perfect.
Any help is appreciated.