ActionScript 3.0 :: Use Tweener To Extend Oblique Line?

I can use Tweener (caurina) to make a straight line grow horizontally from zero length to some given length, like this:

(after creating a horizontal line...)
line.scaleX = 0;
Tweener.addTween(line, {scaleX:1, time:1});

This works nicely. The method also works nicely for a vertical line using scaleY. However, I want to do this type of tween with an oblique line. The problem is that tweening both scaleX and scaleY results in a line that not only extends but also grows from very thin to the intended thickness.

Is there a way that I'm missing to do a Tweener extension of an oblique line (preferably not 45 degrees, that has too much potential for being a special case). If not Tweener I'm definitely open to learning a different tweening method.