Something similar was coming up recently in my meditation practice, where I'd be aware of a vague impulse of a thought or idea arising before it became verbalized. Then I realized that I had had that experience before, when I was a kid and playing music a lot, where I'd notice the sensation of a thought beginning to arise but would put it away before it could get verbalized, since playing music needs a lot of attention and discursive thoughts will certainly make you mess up.
I'm not really trained in Zen, but in reading a book by Katsuki Sekida a while back he referred to thought impulses by varying degrees of 'nen', with the first 'nen' being a thought impulse of pure experience before it is recognized by a second or third degree 'nen'. This sort of felt related to that experience.
I can't think of a way that it could work without invoking the metaphysical.
From https://plato.stanford.edu/entries/incompatibilism-arguments...
"Free will…is the power of agents to be the ultimate creators or originators and sustainers of their own ends or purposes…when we trace the causal or explanatory chains of action back to their sources in the purposes of free agents, these causal chains must come to an end or terminate in the willings (choices, decisions, or efforts) of the agents, which cause or bring about their purposes. (Kane 1996: 4)"
That might be metaphysical, but I don't see any other way free will could operate - that is, if it exists.
His main argument is that we have two causal models to understanding the world, direct physical ones and "agent based". The first is good for figuring out a thrown rock is about to hit you and the agent based models are important for understanding things like a tigers sneaking up on prey.
Wegner proposes that when we apply this agent based model to our own actions we come up with the illusion of a conscious will. This is essentially the same as your post-hoc justification.
This I cannot achieve unless I'm staring at a white computer screen up close.