The following is the routine for using softbodies on characters and then painting the goal weights.
Bind the skin first.
To make a skin a soft body:
1 Select the skin.
2 Select Soft/Rigid Bodies > Create Soft Body to display the options window.
3 From the Creation Options menu, select Duplicate, Make Copy Soft.
4 Turn on Hide Non-Soft Object and Make Non-Soft a Goal.
5 Set Weight to 1. The lower the Weight, the more the skin jiggles.
6 Click the Create button.
7 Click on the skin with the left mouse button.. in the quick menu select the copy of the skin under paint and let go on goalPP. Make sure you are in leaf select mode or you may not see anything under paint.
8 You can now paint in lower values at the cuff over your character's pants so that they jiggle as the character moves.
You'll probably want to add a gravity field and tweak the envelope settings on the softbody surface.