You could just change the file extension from whatever it is now to .j2b ...
If you aren't planning on using the .j2b files for anything.
Even an .exe file would work if you wanted to do that.

Oh well, if you want to convert, say, an .mp3 to a .j2b here's my instructions.
- Get OpenMPT, this is a free module tracker program that works for Windows.
- Convert your .mp3 to .wav, this is the format we will use on OpenMPT to eventually plug into your .j2b file.
- Implement the .wav file into an OpenMPT project as a sample or an instrument.
- In the sequence editor, place the .wav sample as a note on the first line of the first pattern.
- Create enough blank patterns so that the music module is long enough to play the full .wav file as a sample.
- Once you tested it by playing to see if the mod works, save your project as a .mod or one of the formats cooba mentioned above that can be used with mod2j2b.
- Use mod2j2b.
- Voila, I think you would then have a .j2b which can be opened with OpenMPT or vanilla JJ2.

Hm...

Actually how about considering the new OpenMPT can actually edit .j2b files, instead of saving your project as a .mod file, just save it directly as a .j2b file and you won't need .mod2j2b.