Create Master Property with script

do you mean that ?

from Victoria (@FakeGreenDress) | Twitter

function R(P) {
if (P.numKeys > 0) P.addToMotionGraphicsTemplate(C);
for (var d = 1; d <= P.numProperties; d++) {
R(P.property (d));
}}
var C = app.project.activeItem;
var L = C.layers;
for (var i = 1; i <= L.length; i++){
R(L);
}