[morzh]

If this is the case than it works on the same principle as all those "touch" brightness regulators or channel switching on old TVs or "On/Off" touch switches.

I have some around, like the lights in my bookcase or china cabinet. So Sam's question is valid. Though I never saw things that wouldn't work anywhere in the house. I guess it is a matter of the design.

So coming back to the sch, you could play with the value of R703 (might want to increase) and R702 (same thing). Especially R703 - this dictates the input impedance.
As a measure, try to find a "Super-Beta" transistor (those capable of working with microcurrents and having Beta around a 1,000) - this will increase the input impedance a lot and might make it work where it wouldn't before.

http://www.mouser.com/ProductDetail/Fair...8DGTVOs%3d