Yes, you can use polypropylene strings, you can open the string with a needle and use the single wire, or 2 or 3 to make body or what else. The material - as you know - it is lighter then water and doesn't absorb. I use it for everything: wings, parachute point (I dont know the exact name), body.
But (probably) you can't use the poly rope that you can buy everywhere... that rope is too thick.
I'm lucky, becouse I live in a city where there are a lot of tissue factories and they using poly very often... it's a great material