Note: This will require two controllers, the game will not let you unplug and plug one controller repeatedly.As with most games of this type, create two characters, the one you intend to play and one to be used as a "Mule." Put them in seperate saves with seperate names and (even better) seperate species.
One of the two will need some amount of money to start.
Simply start a new two-player game, load both characters and give all of one character's cash (And/or items) to the other and save that character (not the Mule) then move everything from the main character to the mule and save that character without saving your main character.
Now simply end the game and start a new one, loading your main and mule and repeat the process.
(It is much faster than walking back to the Caller Keeper)This sort of trick can also be handy for giving new characters a big head start.Note that you cannot duplicate Keychains or Booster Packs