That's an interesting idea John.
I used to use conductive silver paint on PC boards many moons ago. It actually worked fairly well. I am not sure how this new stuff would hold up to movement as the rails or layout expand and contract, but I do think that it's worth a try for those joints that you wouldn't solder anyway.
I just run extra feeders directly to the turnouts. If you try the pen, please let us know how it holds up over time.
Karl
The mind is like a parachute. It works better when it's open. www.stremy.net
Andy Sperandeo MODEL RAILROADER Magazine
If you're up to painting figures, you could put a LED 'lantern' in a yard worker's hand and power it with two conductive stripes under the painted-on clothing. Lots easier than trying to hide a pair of wires inside an HO scale sleeve.
Some experimentation might be in order to determine if there will be any compatibility issues between the materials in the figure, paint and conductive pen.
Chuck (modeling Central Japan in September, 1964)