Battery Powered Capacitive Touch Controlled Paper Piano

So I have this:

It is essentially this:

But I'm trying to power it from a couple of 3V coin cells rather than USB. However this seems to create some problems with the ground, I was mucking around and found I can only get it to work with this huge roll of solder attached, which will only work when on my leg through my jeans, and not when I touch it directly with my hand (see video). I'm quite confused.

Is there a way I can get this to work without this object to ground it?

Thanks,

Simon

Having done some testing I realised that anyone can hold a wire attached to ground and that grounds it, but it can't be the person playing the piano or it doesn't work.