If you mean loading up the Linux kernel etc - i.e. the actual process of starting Amithlon, this may well be possible.
However, if you mean having your entire Amiga environment on the keychain drive too, so you can just take that to any machine you happen to be near, then the answer is "unlikely". The only possible way to do this would be to produce your own customised ramdisk image, and have everything you need to run loaded into memory when you boot up. Once Amithlon has started, you would no longer have any access to the USB drive.