One more update.
OK, so I've discovered the cause while stumbling around to answer another unrelated question...
This is the part that's in the S model only
And in the SL/SV:
The S model vehicle control module (VCM) is labeled as "without B mode". Also, apparently, without cruise control. Also note that this grouping of parts only spans 2013-2014, the only models that held Cruise Control hostage to the SV/SL trims - 2015+ finally included it with all trims.
So, the solution here may be to crack open the VCM and reprogram an EEPROM with the code from a SL/SV model - if possible - or to find one from a scrapped 2013/2014 SL or SV, and plop it into your S, then wire up a switch panel. That makes it a lot more costly, but it may now be possible!
Also stumbled across this little tidbit:
http://www.plugincars.com/nismo-tuning- ... 27600.html
Hacking the VCM may be a cool project.