How do you set path length

Does anyone know how to set the length of a path in a Solidworks sketch?  I know that in Pro-Eng you can select a number of lines (ie path) and then set their combined length.  A few of the line or curves in the sketch need to be uncontrained so they can change when the overall path length in changed. 

Application is I am trying to model a section for a bellow and need the bellow folds to compress when squeezed but the overall material or section length can not.

Thank in advance for your help

SolidworksSketching