Can't help you out, but if that idea ever leads to something let us know.
![Smile :)](http://gamesas.com/images/smilies/icon_e_smile.gif)
The effect I'm looking for is basically the same animated shield bubble shape, only instead of being a whole bubble, only the edges of the bubble are visible and the center is completely clear. It would appear that way at close-ish range, but not at long range, but I figure it doesn't matter quite as much what NPC-sized objects look like when they're really far away from you... this would also mean that any shield you have around yourself would be pretty invisible in first-person view.
The way to accomplish this would be to black out the alpha channel on the fullsized texture, but leave the alpha on its MIP maps at normal brightness. I have already accomplished a similar effect using this technique, using it the opposite way (leave the fullsize alone, black out the MIPs) to create a shine effect for a moonstone, by applying the altered texture as a glow map on top of the base moonstone texture. Like the shields, this effect only works at close range, but it does work. Unfortunately I don't have pictures, but I did notice that it made the edges of the model's polygons look sharper, so this would need a really high-poly model to work as intended.