We have had some success with using a hose into one of the heater hoses (direcred back to the block,) remove the header tank cap and pour water into the engine that way. Take it slowly and wait for the water to overflow out of the tank, then refit the cap. It's tedious but it has helped us.
Fill the system slowly with your coolant, have the blled screw open, when a good flow of coolant escapes screw the bleed screw back in. Fill the coolant system up to max. Run engine. Allow the fan to kick in once and turn the engine off. Allow the engine to cool down for a good few hours. Refill coolant system a little over the max mark, and leave the cap off. Next, undo the bleed screw and wait unitl the water level has reached the desired level, screw the bleed screw back on, replace expansion cap. Job done