Ok,
Can it be simply three ingredients;
a proper seeing that ‘I’ am the problem. Not that I have a problem, or am “a” problem, but I am “the” problem. I am the threat to actual physical humans.
Biological Altruism is automatically triggered, as it’s main function is to sacrifice the individual for the safety of the offspring/group.
As ‘I’ am both of these, ‘I’ happily allow this event to take place.
Asking for a friend 
Is biological altruism automatically triggered or does one make a decision to activate it?
I think it both, the “harmless” part of “happy and harmless” is us getting out of the way.
It seems that it’s not that altruism is a mystery, it the first point; actually seeing that ‘I’ am the problem.
Not I have made some mistakes, not that I have otherwise failed so “why not?”, but literally and completely that I (the one writing this) needs to disappear completely for peace in this lifetime to become apparent.
This sounds very sensible to me.
Thinking about it being an instinctual action it seems it would be both automatic and of ‘my’ doing at the same time. And equally ‘I’ get ‘myself’ to a point where it is out of ‘my’ hands. All these descriptions depict the same 1 activity. I was thinking about this a while ago and it seems that it is about arriving at a place where all these things somewhat unite, then it happens. This is why it seems impossible to follow a recipe there, because in doing so I am separating this 1 decision into its constituent parts and then trying to act out 1 part after the other and so 1 part of ‘me’ remains separated.
Since asking what is in the way of ‘self’ immolation, far more has become aspects of 1 activity. Twice now, I have been surprised at being happy without and effort. Well, there is effort, but not specifically in that moment. More a general affective effort.
I agree is seems impossible, as if I knew exactly how to do that “one thing”, then I would just do it, right?
The recipe is morphing and changing depending on how closely one can experience the edges of ‘me’. (As you have previously put it).
It’s becoming quite interesting how I can seemingly flip any script these days simply by realising that “hey! Here is a moment I could become free in!”.
Which is the original intent of HAIETMOBA, the persistent willingness to not settle for anything but living the PCE (or pure intent).
Last night, I began to see how important having a happy vision of oblivion is. No one in their right mind would willingly walk into a dark, foreboding “unknown”. A bright, happy and welcoming one is naturally appealing.
Indeed, armies around the world indoctrinate soldiers to believe in the glory of self sacrifice.