This is how I planned on adding an s88 contact point as needed in hidden areas of the layout. The advantage was that I could simply glue the assembly down next to the track without having to lift track, cut rails and relay the track.
A big disadvantage was that track cleaning devices were likely to destroy the switch or get hung up on them.
Antonio Martinez has a much simpler technique using aluminium foil. I am abandoning my experiment and have started my first Martinez type contact. I stuck a length of packaging tape on one side of some foil (thus insulating one side), then cut it out with a tail of bare foil that I twisted and fastened into a Märklin socket for easy connection to the s88 lead. Here it is, insulated side up.
I can them simply pin it down over one side of the rail so that it cannot touch the center studs and covers one running rail. If it wears out I can easily make another to replace it.
Update: These tin foil switches worked without any problems for over 9 years. Even then they did not fail, they were taken out of service as I dismantled the layout.