The lift pump is what supplies the injection pump with fuel, you need to plumb into the fuel system before the water seperators, and fuel filters, so you have filtered water free fuel coming to the injection pump. The injection pump multiplies the fuel pressure from low pressure, to high pressure necessay to spray fuel out of the injectors. Diesel fuel filters are usually about 10 microns, so gasoline filters won't adequately filter particulate that can harm an injection pump. Once you understand the process of how fuel is delivered it makes sense on why things need to be done in a certain way. Having to have an injection pump rebuilt is very costly, so I wouldn't recommend by passing the fuel filters, not worth the risk IMO.
Shortcutting is a way of increasing risk, without much margin of gain. WD 40 sprayed into an intake with electric heat grids will end the same way as ether will, likely an explosion. The intake manifolds in diesels have zero fuel in them, so inducing fuel where there may be heaters, won't end well. The old CAT engines with pony start motors, ran the exhaust from the pony motor through the center of the intake to preheat the intake air. In lieu of a pony motor for intake heat, many manufacturers used electric grid heaters to heat the intake air up. As ambient air temps fall below 40 degrees the difficulty of starting a cold diesel engine is drastically reduced, hence the need for glow plugs, or grid heaters in the engines.
In winter I have heated up the intakes with a torch to aid in warm air getting into the engine allowing it to start easier, if an engine was particularily hard to start. Of course block heaters also allow the iron to remain warm so that there is easier ignition of a cold engine too. Warming the coolant with a block heater will aid in cold start success also.
Diesels also need to spin over fast to maximize heat in the cylinders to ignite fuel, weak batteries, or a dragging starter won't allow enough starter RPM to ignite fuel in a cold engine. When the starter is slowing down, the likelyhood of a cold start is reduced expotentially. As Tim the Toolman Taylor says, "MORE POWER".........
If I'm spinning a diesel for a cold start, I like to either have a jumper from a running truck, or a large battery charger in the neighborhood of at least 200 amps while spinning it over. I learned a long time ago that less than 200 RPM with the starter won't start most diesels, especially if cold.