I designed this screw type leadout, the dragonfly,

only for the unlimited adjustments that it offers, not because of the wingtip shape.
About sliders.
They don’t have to be straight.
They can take on a radius that resembles the shape of the wing tip or just a simple arch.
As long as both pieces have the same arch or close, the fixed wood that the adjuster follows AND the adjuster will “seat” and will also work fine.
Note. The adjuster could be straight, but that would require having a vertical pin at each end of the adjuster. The adjuster would have to ride in an upper and lower track or groove. Not complicated and this can be accomplished, but more difficult to make and describe. Seen blue in the “simple” drawing.
The issue is the exit or line tubes. They won’t be pointing towards the bell crank if moved in either direction because of the arch. See single arrow pointing to pivot where the leadout tube is attached.
This issue can easily be solved by how the exit tubes are constructed. They will have to have a shorter vertical piece of tubing soldered to the primary horizontal pieces, allowing for them to free pivot. Simple actually.
Now, when assembled, doesn’t matter where the slider is placed, the exit tubes will pivot with line tension.
Quick drawing, but you can get the idea. Well, almost.