My own method is as follows:
For lower legs etc:
Roll out some putty (currently favouring grey stuff) andthen press it thinner into a rough shape and size.
make a trapezoid shape, with the top narrower than the bottom
then attach the top to the waist area and let gravity kick in and shape the folds.
For torso's, add a thin amount to the armour and smooth it into the plates. I then use a metal pointy pick, and water, to push some depth into the putty and shape it round areas where folds would naturally occur.
Hope that helps and might be able to get some pictures up later