Flash 8.
stroke.scaleType
Property; a string that specifies the type of scale to be applied to the stroke. Acceptable values are "normal", "horizontal", "vertical", and "none".
The following example sets the scale type of the stroke to horizontal:
var myStroke = fl.getDocumentDOM().getCustomStroke();
myStroke.scaleType = "horizontal";
fl.getDocumentDOM().setCustomStroke(myStroke);