As you can see the HiHat pedal jack is stereo, that is it requires three wires: ground, power and signal. It can be connected to either low or high impedance input. A 100k pot will work with both low and high impedance pedal inputs provided everything is wired correctly.
Now things are getting more clear!
This http://edrums.gl.tter.org/ tutorial is working with mono and I did it the exact same way. 2 wires from the poti to a mono plug and thats it.
So i guess whats missing is the power signal, whereever I should take that from... I bet I'm not the first one using a slide-pot for a hihat pedal. Do you have examples from previous hihatpedals with slide-pots somewhere?
Sorry to keep you that busy with that stupid problem