I've done it, pretty sure I posted pics of it too.

Maybe a search and you could find my pics. Anyway, here's how I did it.

I cut two lengths of tulle, I think they were 4 inches difference (i.e. cut 24" lengths and 20" lengths - I'm just throwing numbers out here.). Cut the v-cut on all ends. Tie on a long strip with the slip-knot method, but stagger the ends by an inch or so, that way you will have 2 different lengths, as in, the 24" strip will have one strip of 13" and one strip of 11" from the one strip you just tied on. Now, take one of the shorter strips, you're going to tie this one with a square knot

*around* the tulle strip you just tied on, you're not tying it around the elastic. Slip one end inbetween the tulle and the elastic, stagger the ends and tie the square knot. This way you end up with 4 lengths of tulle coming from the one spot on the elastic.

Boy, that's tough to explain. Let me know if you have any questions.