I know this is an old thread, but I found a way to extract everything without doing the pawn trick. You must download a program called Umodel. By itself, the only thing that Umodel can extract from a .ukx file is the .psa (animation). In order to get this to work you must have all the files (.ukx, .usx, .utx, .uax). When I create new mutators, I crunch every one of these babies into one .u file. Once the .u file is created, I can discard all the other files. Umodel will extract everything out the .u file (.psk, .psa, .mat, .wav, .pskx, .dds, etc.) In case someone wants to know how to place all these files into the .u file, simply rename your package files to same name before you compile. ex.: myweapon.ukx, myweapon.usx, myweapon.utx, myweapon.uax . Of course your .u name will be myweapon.u. Once you compile it, all the other files gets saved inside the .u file. Hope this helps.
This is what the extraction looks like: