IDEA!!!
two words shell scripting!
the download would just be a folder with an exe(for mac) and a batch(for windows) they'd be installers that you use with would grab the materials from the internet using download routines, and then place them in the corresponding folders. ie. application support on a mac, and then download the actual game to the desktop, and the games coding targets the folder in application support we downloaded using the installer, the installer than deletes the folder it was in, so that it only downloads once, and would also avoid piracy!
It's all theoretical of course, but I'm sure it will work! We've just got a bit to learn, and the great thing is that it would work for every language. Â
and you can't beat that!
EDIT: tell me if you actually would use this, it wouldn't require you to learn anything, just change sprite paths.