mic strategies?

An acquaintance has asked if I could help him make a recording of he and his wife singing a song with fiddle. It doesn't have to be super high quality, but I deal mostly with line-level and the only mic I have is an SM-57 vocal mic. What's the best way to mic a fiddle? Some kind of contact mic? Omnidirectional room mic? Do any of you fabulous music nerds have any suggestions, or gear I could borrow?