Lester Banks notes a AERender, an AE render droplet for OS X:
"With AE AE app from Andrew Hake, you can run multiple instances of After Effects on Mac OS X. The application simply automates the process Todd Kopriva noted which is to start After Effects from the command line with the -m switch, this command line trick will work on both mac and windows os’s."
AE Help covers the same ground and has a large number of additional tips to Improve performance. Andrew made a quick demo of AERender & AEae (both available in his labs section):