Wow, thanks for your quick response. I've been looking at ways to get more volume from my AM transmitter, and whilst Stereo Tool is able to get good volume by using multiband compressors, it just doesn't compare to the louder commercial stations (unless I overmodulate my transmitter, causing distortion and splatter).
The phase rotator doesn't really seem to do much to help with the negative peaks. Also I couldn't find any Winamp plugins that can perform APL.
I was considering implementing this hardware APL circuit
http://www.bruhns.us/APL/APL.html, but being too lazy, I thought I might suggest a new feature for ST. It means less hardware, and software might perform a better job than analogue electronics. That particular circuit has a polarity switch, so hopefully you can also implement something similar in ST.