While poking around in the Tk Docs, I noticed Tk::Photo can take a -data option, I was attempting to see if this could lead to a solution by using Imagemagick to generate an image in memory, and use it as the input for the -data option, and just update it via a configure, unfortunately I can't figure out how to get Imagemagick to output the image data in a compatible format (it's ImagetoBlob method doesn't seem to do it quite right) I'm not familiar with any image packages other than Imagemagick, but if you are this may be a valuable route to explore, as you will only have a single image to update.
Also tried to do a simple writing an image with Imagemagick, as it seems fairly quick at it, and can draw primitives directly as you want. Eh, I'm a little to tired to try offering advice, can't even get my test script to function properly. If you're still having issues by tomorow I'll see if I can't beat Tk and Imagemagick into submission :)
Just Another Perl Alchemist