I you have enough time and your cousin don't play that much, ask him to restring the guitar, and buy a new set off course. If it is matter of one week, just practice on the left handed guitar. Practice some one or two string melodies going alternate picking, or maybe going up the neck using two strings at a time. you can also practice right hand strumming, get your pinky little stronger, or do some simple hromatics in django reinhardt style. If you get bored with those, try some power chords, or maybe practice your ear by playing a game where you must remember the sounding of one one and recalling it by heart. aaaah you can do a lot of things, don't worry