No, the solution here is much easier -- be consistent.

https://ftw.usatoday.com/lists/nfl-touchback-rule-fumble-justin-jefferson-solutions

Nowhere else on the field can you advance the ball by fumbling out of bounds.

If you fumble the ball at the fifty yardline, and it moves forward out of bounds at the forty-eight yardline, they still spot the ball at the fifty.

If you fumble the ball at the one yardline, and it goes out of bounds past he pylon, the ball should be spotted at the one yardline.

If you broke the plane before fumbling, which is the only logical reason why the spot of the ball would be past the pylon, it's a touchdown. There's no rule about how long you have to retain possession of the ball after breaking the plane.