To the point: Rather than render out the AO pass within the highly detailed render, simply duplicate the project, apply simple color mattes (no reflections, textures, etc) to your objects, change the settings from best to geometry, and render out. It won't give the full detail of a full AO included pass, but it will do pretty well overall.
This saved me a TON of time. In Ae, I'm able to apply the AO matte and get a rather decent additional shadow that really helps bring it all together. Granted, I'd love to have the computers to just do it all at once, but under deadline with a pretty detailed render (approx 20mins per frame), this worked out pretty darn well. :) Thought I'd pass it along.
Apple XRAID, XServe, 2008 2x3 GHz Quad-Core MacPro, Macbook Pro, XSAN, FCP Studio (7), AVID Media Composer, Adobe Production Premium, Maxon Cinema 4d, AJA Kona 3, Flanders Scientific Monitors, Panasonic HPX250's, Kessler Crane, Glidecam.....
Beer fridge fully loaded.