MechAssault, spliced USB cable, and the USB drive
The project is going good so far compared to my previous attempts. At first I thought it failed when I plugged in my USB drive, but then I realized that I spliced the cable so that the USB drive and the controller would be sharing one USB port on the Xbox (one USB for two devices is a no-no). Here's the shot of how the USB is supposed to look (it's actually on...) and how the screen should look (USB stick recognized as Xbox memory).
After it was recognized and formatted by the Xbox, I connected it to my computer to make the USB drive work with the Action Replay software to transfer the savegame exploit.
In theory the Action Replay software should be able to transfer files to my USB drive now, but it isn't. That's going to be the next hurtle of the project (hopefully only a small one).