Change from External to Internal teeth

[sanddrag]

If I have a drawing of a tooth profile (accurate, involute) in AutoCAD of an external spur gear, is there any way to make this the profile for an internal gear? I don't know anything about AutoCAD but theoretically If you "flipped" it using the pitch diameter as a "curved axis" upon which to "flip" would that work? If so, how do I actually do that in AutoCAD? Thanks.

EDIT: I was just looking at some pictures of internal gears, and now I'm wondering, is it the exact same profile with no flipping? Like a "negative" in a sense. Like if I took a spur gear and put in in a bucket of plaster, and then it hardened and I pulled it out, would I have an internal gear of correct dimension/shape?