I remember your (?) model that did that with an egg shape around an Enforcer.
This is how all cell shading solutions do the outline effect as well, duplicating the mesh and applying a 'push' transform and flipping the triangles, then applying a flat black colour to the newly generated mesh.
Where black lines are needed they just get painted onto the diffuse layer.
When it's done to extremes on low poly stuff you start to see artifacts:
http://www.mobygames.com/images/shots/l/93349-viewtiful-joe-gamecube-screenshot-starting-a-new-game-joe-and.png
For a Quake forcefield, if you wanted to go nuts, you could export the entire mesh plus animations, push it, flip it and then attach it inside the Qc so that it would follow the animations of its owning monster. This would allow you to apply a
.alpha value, animate the skin and apply texture fencing.