what you could try is shut down one engine and vent it while the other one is still running, thereby using its generator instead of the battery. Then shut the other one down as normal.
This should give you a cold and a hot engine for the start. Start the cold engine first, then vent the hot engine if required using the generator from the running engine.
It is probably not a practice recommended by the manufacturer, but it should work on twins.
brgds, S76Heavy