You can definitely give a live mouse a try -- the size of the mouse would depend on the age of the snake (you didn't mention in your post whether the snake was still a baby, or a yearling, or an adult...). Just tell your friend to buy a live mouse that is slightly larger in size than the thickest part of his snakes body, and get him to dangle the mouse in front of his snake with feeding tongs (not fingers!
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). Most likely his snake will snatch it right up... If not, he may have to try scenting these mice with a lizard (basically this is just rubbing the lizard against the mouse to rub off some scent).
Let us know if it works out, hope that helped a bit
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Jen