I once put some aluminum duct tape completely over the touch pad of an old laptop to see what would happen. Turns out it induced enough "eddy currents" to make the mouse move around the screen without me touching it--in a way, visualizing the currents!

I connected the foil to ground using a small strip of the tape to the ground metal of a USB port on the side and it disabled the touch pad.

Looking back, it would have been interesting to code up a program to record the movement of the mouse as a trail of pixels...

If you ever want to do this keep in mind to reconfigure the mouse as a digital pointing device (tablet like), otherwise the mouse acceleration will mess up your position measurement.

No, you need roughly a small human's worth of ground mass for most capacitive touch sensors to register a touch.

How do capacitive pens work?

You electrically couple to the pen, unless they are active devices, in which case they generate a signal.

That can't be, they work with gloves and things. My gloves even have a thing at the end that works with the touchscreen.

You’ll have to be more descriptive for me to have any hope of answering.

If by your gloves have a thing at the end you mean a patch of special fabric, yes, that fabric conducts from your skin to the screen.

Tape a wire to the trackpad and hold the wire?

ground mass?

If you don't have ground human presumably you can substitute ground beef or ground turkey.

Could probably make a small stand with nubbins from touch screen pens as the feet.