Forcing the game to use Targas instead of JPEGs

[GreyWing]

I've noticed that some of the higher resolution textures in JK2 are compressed as JPEGs. It's a clever way to reduce texture size, but if you look closely you can see the compression artifacts and they make the model look less detailed. I've been able to smooth most of these out (and tweaked the colors a bit) in Photoshop but the game won't recognize the textures unless they're JPEGs. Is there any way to force the game to read Targa textures instead of JPGs?