I have been retrofitting a few older 2.6"-4" dia cardboard tube rockets with rail buttons and wood screws.
These all have 1/8" ply centering rings. On one model, the night before a launch, I installed the aft button so that the screw came out just below the aft centering ring. Mixed up a batch of 30 min epoxy with milled glass to make it thick enough to stay in one place and not run. Built up a smooth epoxy fairing over the screw, blended out to the centering ring, potting it into place.
After that epoxy kicked, I installed the forward button just above the forward centering ring. Used a long stick to apply the filled epoxy over the exposed body of the screw in the same manner as the aft screw, only not quite as neatly. Looks and feels to be more than strong enough for this 4" x 78" rocket in any flyable wind situation while on the rail.
There are obviously other and better methods when building for rail buttons from the get go, but this is a pretty easy and quick way to retrofit an old model with launch lugs.