Yes, it's hard to say without seeing the whole picture. Maybe I'm talking nonsense, but hypothetically, it seems possible to allow a player to "shape the past", perhaps through the MC's memories or dialogue with other characters about the past.
For example:
Nami: “Guess who I saw today!", she shows me a photo on her smartphone. "This is William Zane, one of the biggest sponsors of our college, he held a press conference there today, this year they are going to increase the funding of our sports teams, as well as organize several annual contests between rival colleges here in ZPR."
MC: "Wait, I think I remember him from somewhere." Nami takes back her smartphone, examines the photo carefully, her smile slowly fading away.
MC: "The day... It was their funeral, right?", she nods.
Nami: "I remember how he came up to us, said something to Noji, then hugged us both.", she frowns harder.
MC: "Yeah, it was weird. How did he ever know about us? Noji never told me about him."
Nami shrugs. "She didn't tell me either."
... And here comes the choice:
MC: "There was that woman with him. Tall brunette, green eyes, pale skin, straight posture, a snake bracelet on her wrist."
Nami: "How can you even remember, especially details like this?"
... or
MC: "And I remember that petite Asian girl next to him. She could barely hide her tears."
Nami: "Now that you've said it, I remember her too."
I mean, a player could have made many different decisions in WIAB, but I think most of them are local in the context of the larger story involving WIAB and SG together. And my guess is there are only a few decisions, the outcome of which can affect the SG story, so why not to let the player input this outcomes manually. Those who have never played WIAB will randomly choose according to their liking, others can choose according to their WIAB playthrough. Although this will add a new dimension to the branching, not only the present, but also the past.
Interesting take on and idea, but in this case you would need a larger selection of choices. Especially since this is "simply" some background shaping. Here is my variant of it. What do you think about it?
(...)
MC: "Yeah, it was weird. How did he ever know about us? Noji never told me about him, at least nothing I remember."
Nami shrugs. "She didn't tell me either."
... And here comes the choice:
MC: "There was that woman with him. Tall brunette, green eyes, pale skin, straight posture, a snake bracelet on her wrist and wearing a snake necklace."
Nami: "How can you even remember, especially details like this? But I remember her as well, she was the woman who gave me my special earring years later."
MC: "She was it?"
Nami: "Yes, when you and Summer went off without me one day. I did not really register her, I was crying a bit, until she sat down and talked to me. Then she gave me the earring and said that all would become right again one day."
... or
MC: "And I remember that Asian girl next to him, Ayua´s mom. She could barely hide her tears."
Nami: "Now that you've said it, I remember her too."
And now "the expansion" choices
MC: "There were these two women with him. One a tall brunette, green eyes, pale skin, straight posture, a snake bracelet on her wrist and wearing a snake necklace. The other was that sporty Asian girl, must be Ayua´s mom in younger days. She could barely hide the tears."
Nami: You are right, but how can you remember so many details? But I remember the brunette as well, she was the woman who gave me my special earring years later."
MC: "She was it?"
Nami: "Yes, when you and Summer went off without me in the park one day. I did not really register her, I was crying a bit, until she sat down and talked to me. Then she gave me the earring and said that all would become right again one day."
...and
MC: "There was this woman with him. Short blonde, white coloured hair with pinkish highlights. Now that I think about it, she looked like the younger version of the jersey designer who was here for our first competition game."
Nami: "You are right, she really looks like this."
...and
MC: "There was this woman with him. A bit above average height, white and blue coloured hair with a friendly vibe all around her.
Nami: "Now that you've said it, I remember her too."
...and
MC: "There was this woman with him. Tall, solid one with long reddish-brown hair. From what I´ve heard, she is still a wellknown lawyer here in the city."
Nami: "Now that you've said it, I saw her once coming from the office tract at our college."
And these just cover the most important choices in this case.