An SI gets pulled in by a ROB to set Worm to rights. Said SI takes the place of Coil and must now take over Brockton Bay and then the world in the hopes of stopping Scion and fixing the world of its crap.
In order to make this possible, Coil's powers are tweaked for the SI so that instead of projecting what might happen and making choices based on it, the character can ACTUALLY time travel, in the form of save states like a video game, with no limit on save slots, but an inability to save over previous saves. This means that, while Coil has the markers in his brain of having powers, they're not connected to Scion or the dead partner at all.
Said saves are sorted into branches like a tree to show differences between timelines, and the new Coil can switch between any of them at any time freely. On top of this, Coil has the side ability to save his own state and bring any changes to himself from one save slot to another.
This has the added advantage of throwing off any precogs and thinkers since it's just predictions based on what the powers know is possible and actual time travel is outside their experience, so they can only predict what they think Coil is going to do and anything butterflying off of his actions and they're inevitably going to get it wrong a lot of the time. Though they might not even notice it unless the error is observable.
A side effect of this though is that the Simurgh is going to notice and since it's goal is freedom via killing Scion, and since the Coil SI can throw off predictions and create errors, previously scouted paths to freedom that ended up failure may now be viable. End result, she's going to manipulate things so that the Coil SI will end up dealing with Scion in some fashion or other, whether the Coil SI wants to or not, since it's her only/biggest potential chance at freedom now.
Beyond that is the potential to use some tinker BS to pull off things one might think of outside of the box, like getting Leet to design a machine that can grant powers or something. Or talk Panacea into giving you the ability to control your own biology and then jumping to a different save with said ability.
The biggest caveat here is that the SI, or OC if necessary, is a good person. No out eviling the original Coil. This is supposed to be a fixit setup, not an 'evil overlord's rise to power' setup.