One thing to note is that the man would probably harm, not help, his chosen charity (in expectation).
If it was thought that the charity had encouraged the "really extreme altruism", or if it was simply thought that the charity was the sort of thing that fanatics like that liked, the charity would have serious problems attracting others' work or donations, since most people fear fanatical and suicidal mental states. It would need to refuse the money, and refusing the money wouldn't be enough to prevent serious damage.
You could just split the money among a whole bunch of different charities. That way no one in particular is shamed by the news stories that result.
In secret, an unemployed man with poor job prospects uses his savings to buy a large term life insurance policy, and designates a charity as the beneficiary. Two years after the policy is purchased, it will pay out in the event of suicide. The man waits the required two years, and then kills himself, much to the dismay of his surviving relatives. The charity receives the money and saves the lives of many people who would otherwise have died.
Are the actions of this man admirable or shameful?