All you need to do is move Minecraft to the USB drive and make a symlink on the system pointing to it.
Assuming the drive letter of the removable device is T
xcopy /E /K %APPDATA%\.minecraft\*.* T:\Minecraft\
ren %APPDATA%\.minecraft .minecraft_orig
mklink /D %APPDATA%\.minecraft T:\Minecraft\
edit: okay, yeah, that .bat with a local overridden appdata variable is definitely easier. that article doesn't need to be anywhere near that verbose to explain that though.
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L.A.W..---- / ....- -- / .-.. --- .-. -.. / ...-- -. --. .-.. .---- ... .... / > ---... -..