As you know the capacitive touch screen, unlike the resistive, needs to feel the electric charge of your finger. While in the resistance, which is formed by a membrane mobile, simply touch the screen with any object, the capacitive screen works only if you feel an electric charge, then the pen must be strictly conductive.
For the realization I used readily available materials. Of course you can wander with the imagination as rigualda the body of the pen, the important thing is that it is metal.
An old slat curtains. (the one that stretches with two holes at the ends)
A clip of a pen to throw.
A piece of foam anti-static. (This is the gift you can ask a store of electronic materials. In short, is the foam that protects the pins of the ICs from electrostatic charges.
Cut the pipe about 100 mm batten taking the good with the end cap holes.