Put a longer neck on. The "scale length" people talk about is the distance between the bridge and the nut; that is, how long is the length that vibrates? You might have to use different strings.
You wouldn't HAVE to put a bigger box on the longer neck, but it wouldn't hurt either.
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You wouldn't HAVE to put a bigger box on the longer neck, but it wouldn't hurt either.
http://en.wikipedia.org/wiki/Baritone_guitar
-WY