There has to be another file associated with the .wad
Whether it be a .hed, .dat, .whatever or in the case of thaw sound paks the sfx pak is the 'wad' and the 'hed' data is found in the sfx_dat.qb
The other file stores the entries of each file; checksum, offset and size for each file in the wad.
Unless there is padding between each file in the wad and/or each file in the wad has a fourcc magic number doing this manually would be impossible.
