Over the years there have been different techniques attempted to get longer bones. However as of this writing (2011) only the technique where you break the bone and gradually lengthen it is reported as practical [Dahl, 1996].
This technique is called mechanical distraction or callus distraction. There are different devices used in mechanical distraction, but all of them are based on the similar concept that you break the bone without severing the periosteum and then slowly elongate the break over time (callotasis or "callus distraction") and/or adding some bone taken from eleswhere and move it into the break ("bone transport" or "bone graft") .
The lengthening devices/techniques used as of 2006 according to http://www.wheelessonline.com/ortho/discussion_of_limb_lengthening
are
Additionally there is in the literature
http://www.ilizarov.org.uk/
http://mednews.stanford.edu/stanmed/1999summer/magician.html