I have no experience using worlbla's but taking a look at the tutorials I do have some ideas.
Once heated the material can be merged (that is what they say) So I suggest that you make the skirt in parts.
You will need the model of the pelvis ready atleast and set up at the right height that you need the legs to be.
You'll need a heat gun.... I think a hair dryer works too. These days they are bringing out hair dryers that can power a nasa jet! Plus it is more controllable. A paint stripper's heat gun at the lowest setting might still be too hot for these, meaning that you show it for a very little time and then get to work. It can be unforgiving if you leave it in a little longer and you might get holes.
Heat and fold is going to be your technique. You'll also need to find a way to avoid your fingers/tools from sticking to the warmed up plastic.
For the front... take a rectangular strip, warm it and fold in 8 parts on the length of the shorter side. You should get a saw tooth formation that is extruded all along the length of the strip... I've done one for just 2 saw teeth.
Now take all the teeth at pinch them together (somehow... not a binder clip!) and use the hair dryer on high air blowing speed to shear the folds along the line of the pencil tip.
You can use some tool to pull down the folds as they get warmed up... make sure not to pull and tear through the folds. Another tip would be to fix ONLY one side of the sheet (length wise) so that it doesn't move around. If you fix both sides of the length then you will not be able to stretch the folds beyond a limit. Pulling down the folds will cause the sheet to curve and reduce the linear length of the sheet.
For the creases on the topmost fold you can warm it again and run a rounded tip tool from the right and pull along the length in such a way that it collapses inside. That way you get an additional saw tooth.
Read my cape tutorial for ideas on making the folds around the back:
http://barneyjoseph.blogspot.in/search/label/Cape
By now you should have a fair idea of how to get the bow done. Once you are satisfied with the folds and freckles, warm the sheets uniformly and push them against your model (pelvis) to get a form fitting curve (this is possible as per worlbla's superhero mask tutorial). Then find a way to merge the sheets together.
Good luck and do share pictures of the WIP.
God bless you
