Your issue is not glo plugs. You no start / hard start issue is fuel gel point, which is the temperature point at which the fuel, in your case WMO, fails to flow and atomize.
The addition of heat in the combustion chamber does not heat the fuel at the injector or the Injection Pump. You need fine droplets of fuel to gain the combustion caused by the compression of fuel/air mix in the compression chamber. At -5°C. your chosen fuel is failing to pump and atomize into fine droplets.
Heat is your friend in this case, properly applied to pre-heat of the fuel. If you do not have a block heater, which pre-heats the coolant, which rises the combustion chamber temperature, you will also see benefit from having one.
Alternate fuel such as WMO, or WVO, needs to be pre-heated to 120°F [to 160°F, upper range] prior to the injection pump to be made liquid enough to be atomized at the injectors.
You have a cold engine, cold fuel, at or near its gell point, cold ambient air... to get combustion, you need to rise all those elements to the fuels flash temperature, based on only the temperature rise caused by rapid compression at the top of the compression stroke.. [a few degrees before TDC, actually].
To cure the whole problem.. you have to fix all the elements. Failing to address "frozen fuel" will cause the other elements to fail in function.
You might want to change to a two fuel system. Switch to pure diesel prior to shutdown giving enough operational time for the Injection pump to purge all WMO and run the engine for a bit on pure diesel. Start on the pure diesel system and only switch to WMO when the engine reached full operation temperature. You will still need to address the issue of cold WMO failing to flow and atomize.