You can do this for Brawl, using a black textured object that is slightly larger than the mesh itself, with its normals facing inward only. (Nel's face has an outline, and I'm pretty sure that this is why). This tutorial might work in Brawl when shaders are figured out completely and if dae models even support this.
I saw the Shenron model has an outline.
Ok, BlackJax96, when the time comes maybe you could help. Looks like it'll be a while then... :/