I spoke with them about this (drawcord) and, if I remember correctly, was told they would. I don't remember why I chose not to though. Perhaps it was more $ than I wanted to spend, a time thing, or extra weight. I suspect it was all of those. But yeah, it would definitely add some versatility.
I do remember that doing a customization such as mine was easy as nothing had to be changed to their existing pattern. Just add desired amount of fill and bingo!