Well, here may be one not thought of... I have tried balsa wood under my thread before to cast with a heavier jig for more distance but slower fall. It did work, sorta, but took some time to carve and taper a piece of wood that small. Was also somewhat soft, and thread would cut in if ya wraped too tight. Not sure how much tension is needed to do what ya do. You can put enough on to make a 1/32 jig sink very slow, but takes up too much room and you are pretty much left with a big thread body and tail.

Mylar tubing?? Never tried the stuf so just a thought.