alternatively you could use VEX.
1. create a measure sop (to measure the perimeter)
2. create a primitive wrangle with something like the following code:
//do this after a measure sop
#include <groom.h>
float factorPerPolygon = fit01(rand(@primnum), .5, 1);
adjustPrimLength(0, @primnum, @perimeter, @perimeter * factorPerPolygon);
in above example each curve will be randomly refit between 0.5-1 times its original length.