The only sure cure for the CAP Snap is get a different make of airplane.
Adding -anything- to the outboard wing of a CAP will make a bad situation worse!
The wing-root mounted sharper leading edge devices commonly used on many small planes are a much better choice than doing anything else to the wing.
And in reality, these work by stalling that portion of the wing first, creating turbulence and noise the pilot can hear.
On a model, the noise wouldn't be observable.
For a CAP, the safest thing is never let the speed get low. Fly it faster than a similar Extra or Edge.