Do you have a chop saw? You can build a jig simply by joining a couple pieces of scrap together at a 90 degree angle, clamp that to your saw at the right spot, place the butt *sans butt pad* against the jig, lop off the excess. You can then either cut down the original butt pad or install a new one, like the Decelerator.
First, I'd see if a youth butt-stock could be located as @justmax suggested. If that isn't available, locate a used stock to cut down as per @Sasquatch demonstrated.
Personally, I would if possible keep the original butt-stock original. At some point, if you decided to sell, it could be in your favor to be able to go back fully stock.
For a temporary fix and to see if I like the shortened lop I ordered a regular plate to put on it for now. The stock is a Boyd stock and I really like the colors of the wood so I don’t want to change stocks.
I like the way that looks! Like Axxe said, you should still be able to order a replacement if you royally screw it up, but if you build your jig solidly so it can't flex when you cut, you should be fine to use the method I described above.