Add a keyline to a shape through actionscript?

I have written an inverse mask function that allows the user to draw on the screen and basically erase what they can see... there's a bit more to it than that but it's a live project!
I was wondering if it's possible to:
- add a keyline to a shape through actionscript?
- or Expand the Fill of the shape by a few pixels to give the appearance of a keyline?

Cheers