How to set Free Transform default reference point to top left?

You can record an action with the modal control on (see screenshot) for an interactive transform and use an F-Key action shortcut. 

A script can also do the same with the choice of a custom keyboard shortcut.

transformLayer(0, 0);

function transformLayer(horizontal, vertical) {
	var s2t = function (s) {
		return app.stringIDToTypeID(s);
	};
	var descriptor = new ActionDescriptor();
	var reference = new ActionReference();
	reference.putEnumerated( s2t( "layer" ), s2t( "ordinal" ), s2t( "targetEnum" ));
	descriptor.putReference( s2t( "null" ), reference );
	descriptor.putEnumerated( s2t( "freeTransformCenterState" ), s2t( "quadCenterState" ), s2t( "QCSCorner0" )); // upper left
	descriptor.putUnitDouble( s2t( "horizontal" ), s2t( "pixelsUnit" ), horizontal );
	descriptor.putUnitDouble( s2t( "vertical" ), s2t( "pixelsUnit" ), vertical );
	descriptor.putObject( s2t( "offset" ), s2t( "offset" ), descriptor );
	descriptor.putEnumerated( s2t( "interfaceIconFrameDimmed" ), s2t( "interpolationType" ), s2t( "bicubicSmoother" ));
	executeAction( s2t( "transform" ), descriptor, DialogModes.ALL );
}