My initial thought would be to make the rubberband a seperate scene with a sprite, a tween and an anchor point (maybe a position2d?).
In its (the rubberbands) process function I would have written something like this piece of pseudo-code:
get distance between finger input and anchor point
get angle bewteen anchor point and input
clamp the values to minimum and maximum values, so you dont get overexaggerated results
tween the rubberband sprite the evaluated distance and angle
Just an idea, maybe someone knows a better or more elegant way. You can check the docs if there are functions to help make the calculations or you could calculate it by code with vector math. Here is a really good explanaiton on vector math, if you have not read it already: