Well, it seems that your tcl script is about the only thing around that can do this. If Courage can't show you how to run the tcl thru Tk using the tcl module, I would say switch to a canvas. The canvas can display just about anything, and you can layer the things with tag priorities. The downside is that you will probably have to reinvent the tree, and manually create it on the canvas.

Even Gtk would have trouble with this, because their themes do not extend to every nook-and-cranny of every widget. They setup the themes for the most commonly wanted theme schemes, but the background for the treeview is still not done independently.

You could have done it on a canvas, within a week. :-) It really wouldn't be that hard once you got your design down. Setup an invisible grid on the canvas, and display your tree items as little icons or text. When the tree changes, you will just have to delete everything and rebuild; but the canvas is very fast, so it ought to work pretty well.