You shouldn't need a bypass hose, no need to heat the water in the radiator, its just a waste of electricity. The block heater thermostat should be set below the car thermostat so it doesn't open when pre heating and once the engine is running it will still take a few minutes to get up to full temp.
I'm not sure where to break in to the heater hose as the car is in my workshop so I can't have a look right now.
when you can it would be great to know still waiting for the heater to turn up so i cant start the build yet