There isn't really a simple way to do it. You have to manually modify every method that draws icons. If they are taller than 32 pixels, you will pretty much have to modify the entire way that text is drawn, since that is the default height, and if not the icons would overlap each other even if you accounted for a larger size.
I would strongly suggest you find a program to batch resize them. You are not going to find a script that even resembles compatibility out there to do it. I can make a program to do it real quick. Give me a few minutes.
EDIT:
http://dl.dropbox.com/u/20787370/Applications/IconResizer.exeHere it is. You can resize an entire directory at a time to any size you wish, in either PNG or JPG. Hope that helps. It reads .png, .jpg, and .bmp files.
Output images will be placed in a folder in the programs directory called "RESIZED".