Actually, you can do it with custom blocks. There's already some blocks in Blocktool that, when hit, adds stuff to your item box. For example, you can add springboards or boo blocks...or even have a block that takes away items from your item box! O_O -------------------- Thanks to Wraith for the layout.
Will be glad to test hacks. PM me hack information and download links.
You would just have to program the block, it's probably only about 15 lines of code (added in, 1 command per line.)
If they didn't want to make it public, then they probably won't give it to you. Your best choice is to use ASM.
It's something that a lot of people are scared of, but like learning an instrament, it's not hard, just takes time.