@503,824 (B)
> Isn't that just piracy
How is that piracy? If he's paid for the game there's no law saying he can't take it with him.
@503,826 (C)
> Would you put a car on a USB and make it portable?
A car is portable, if your car doesn't move then it won't do a very good job. Also I'm not sure what you're getting at, but it makes no sense and/or is completely irrelevant to the question.
OP: You can just install the game to USB and it will work fine, or drag and drop the files from the original install directory into a folder on the USB. Running the game will leave registry keys for the game on any device you play it on, to prevent this run the game in a program such as Sandboxie.
(Edited 4 minutes later.)