I am not going to take credit for this one, because I read it in an interview with Tchad Blake.
In Pro Tools duplicate your kick drum track, insert the San Amp plug-in and adjust until you get a thick round low end with some distortion. Now include your clean source track and REVERSE THE PHASE on your Sans Amp track. Continue adjusting Sans Amp Plug-in (especially buzz and low knobs and take down highs) until you hear it sound like it is an octave below. I was skeptical, but works great for a thick kick.