You're asking from the perspective of the MC, but I think this is a player-facing procedure. When I MC Apocalypse World, I'll tell the players to take note of such things (forward, holds, whatever) sometimes, if it isn't going to be used (and used up) immediately. But once they aren't newbie players, it's totally their job. I, as MC, have enough stuff to track. (Though I suppose I give more attention to it when they get a -1 forward.) If they don't care to get that bonus or reincorporate that fiction, then they won't. But because you're always barfing forth more apocalyptica and putting your your bloody finger prints on everything, it's not really the end of the world when that sort of thing gets lost in the shuffle.
And flipping that around, when I'm a player in an AW game, I do make notes of those sorts of things in the margin of my playbook -- there's plenty of room to note stuff like that even if I'm not taking more formal notes on a pad or whatever.
As to the "while keeping the focus on the fiction" part of your question, when I do take those notes, I jot down something like "+1 ongoing when offering Rolfball companionship" or "+1 next time I read Dremmer using the machine Spector made" so that I have the fictional triggers right there with the mechanical effects. That level of detail is enough of a cue to remind me what led to the bonus in-game even if it was a couple sessions back.