This guide worked for me. I made sure to always add an interview for both HBK and Rey Mysterio each week to fill both promo spots. Also at the beginning I did events (charity) for Mysterio in order to boost his popularity to max. I didn't hire anyone or do any rivalries, just added the interviews each week and made sure every PPV I had matches that the final match was Hell in a Cell.
I was able to unlocked it by the end of December. After reading this thread I assumed this was going to take a few hours and be a pain in the ass. However it actually went by quickly, probably within a hour.