There's a tutorial for a somewhat-similar sling at
http://www.slinging.org/articleimages/20/19.htmNow, I can't see details of the sling in the video, but Dan says that he used a four strand round braid for the main length and a five-strand flat-braid for the pouch.
So...just making a guess:
Instead of starting with six strands as are described in the tutorial, start with four strands of tarred bank line. (I'd use at least 126" instead of the 110" that the tutorial uses).
Instead of the three-strand braid that the tutorial uses, I'd use a four-strand flat-braid for the finger loop and a four-strand round braid for the down cord (See tutorials below).
To me, at least, the complicated bit is adding a cord so that each part of the pouch uses a 5 strand flat braid instead of a 4 strand flat braid. The way that I would do that: Cut a length of tarred bankline that is about 2 feet long. When you get to the step in which you 'secure the braid and separate each of the strands evenly into two new strands of (four) strings each', I would lay the 2' cord across the split so that 1 foot of it would follow each side of the braid. Then...I would braid each side of the pouch using 4 long strands and 1 short strand (using '5-strand flat braid #2', see tutorial below).
When it's time to combine the two pouch braids, I'd bury the ends of the 'short' cords inside the core of the four-strand round braid so that there are no ends visible.
Does this make sense? If not, I can try getting a camera to do a tutorial myself. Fair warning, I just bought a new house a few months back and I don't have a workshop yet.
Oh, hey, the tutorial for the four-strand round braid and the five-strand flat braid #2:
Timothy Potter has some WONDERFUL 'how-to' tutorial pages for different braids at:
http://www.seekyee.com/Slings/howtos.htm