I wasn't aware that I outlined a plan to stop everything. I merely pointed out that if Lelouch captured Euphemia he could have tried to use her as hostage to force the Britannians to stop the Fuji Massacre and had a chance to save tens or hundreds or thousands of Japanese who might have been killed by the Britannians at Fuji after he could have captured Euphemia.
And I pointed out that at the beginning of Episode 23 Euphemia made a broadcast ordering all Britannian soldiers (and also civilians?) who heard it to slaughter all the Japanese they could. Thus there was a fair probability that there were other massacres going on at the same time as the Fuji Massacre . If so the fastest way (if it worked) to stop all of them was to capture Euphemia and try to use her as a hostage to stop all the massacres at once. In my opinion not capturing Euphemia to use as a hostage to stop the massacre(s) made Lelouch guilty of murdering all the Japanese who might have been slaughtered after he could have tried to use Euphemia as a hostage.
And I also pointed out that if a leader who values the lives of his followers the least little bit has a chance at the beginning of hostilities, when the outcome is still undecided, to either kill or capture the girlfriend of the enemy's greatest warrior and the beloved sister of the enemy commander, he will certainly choose to capture her instead of killing her.
And I pointed out other practical disadvantages to killing Euphemia.
But that is not the same thing as having a specific plan based on the best possible way for Lelouch to use Euphemia as a hostage.