So the files are already clipping? If yes then there isnt much that you can do, especially if you have to work with mp3's, you can always increase the volume but you will loose more dynamics.
Many software (adobe audition is one of them) have an option to hard limit the output to 0.1db this way you want have clipping, but i dont like the sound that comes out, to noisy for my taste. I personally prefer to have a life that clips for a few ms that a file that it's hard limited to 0.1 and everything is loud.
Also if you re-record the file you want be gaining much dynamics back, from my experience, what ever is lost is lost, and not an easy task to get it back.