Depending how the arm moves and level of detail its really about compositing.
I actually say the demo reel of a guy who made a couple shots of that arm but I cant find the link now.
Simply put make a fully rigged arm stretch and animate it and composite it over the video. You will need multiple rigs in various length and flexabilty. I suggest a spline IK for the long one and adding alot of stretch in the short one.
good luck,
/randy