It wouldn't work as you have suggested but with a bit of extra work you could make it work. Lets assume you've went as far as putting his save on the Usb. What You'll want to do next is download a program called Usb Xtaf ( il leave a link). You may also need 7zip ( il give you a link to it too).
Copy a save from your xbox that is from your account on to the usb. To make things easier make it a different game. Now that you have both saves on the usb put it in Your computer.
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