hmmm using a manual switch for your thermo seems fraught with danger. I have done it once to limp home my old 4wd, but I wouldnt reccommend it for daily use. You get distracted once and it could be too late for the ole a series.....
When I fitted the thermo to my patrol, the fitting kit came with a rubber shim that you put between the inlet pipe on the radiator and the hose. The sensor sat between the two like a sandwich. No screws in pipes. simple really.
Since I gather that yours has a threaded sensor, you either have to go down the custom pipe road like you spoke about, or tap into the top tank on the radiator. This will achieve the same effect as in the top hose.

about the time to turn it on, well I just did mine be trial and error. I had it turn on early, tried that, and just adjusted till i was happy with it and it never failed, the thermo setup that is. the rest of the car.... well its history now thank god.