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Carry the yarn that's not in use back to the area where it will be used by catching it every 3 or 4sts with the working yarn. You can catch the unused yarn float so that it doesn't form a long loop just the way you catch the unused yarn in fair isle. Here's a pretty good drawing of catching the float (twisting the working yarn and carried yarn).
http://www.dummies.com/how-to/conten...-knitting.html