With some help from the file format information jamesster found on Xentax I have made a JAM extractor. For the amount of information it has to process, it's rather fast, but it will hang there for a bit as it processes all the files (so have patience). Without further ado, here it is:
JAM Extractor
Latest Downloads (RRU):
Windows 32-bit
Windows 64-bit
Mac 64-bit
Latest Downloads (Github):
Windows 32-bit
Windows 64-bit
Mac 64