I never wrote a tutorial because the whole process was rather complicated because it was at the best a guess and check process, and you almost never got what you expected. I don't have any documentation on it at all, and I hardly remember it. I can tell you that you can easily find the address of the x/y of the currently held object and the size will be right next to it. But modifying the size has a set of behavioral rules that I spent many hours learning and just don't remember. For example, you can't stretch a "small" piece, it will just float in the middle of the stretched field.
Edit- Try contacting Full Metal Kirby. I believe I taught him how to do it, and he may have some logs or his own files.