I think the braided fishing line referred to referred to by Mark is known as "squidding line" here in northeastern US and is used for surf fishing. It's cream colored and about 1mm in diameter, very strong and flexible. If any one is interested I can see if it's still available. I understand there is a braided monofilament too but it may be stiffer.. Not sure, I don't fish much.
I have a TP with the same shutter and this thread has been an inpiration to try to get it working. Thanks to all.