WARNING! Do not perform these instructions until your work queue is empty. Both times I've tried installing it, it wiped out WUs in progress. I am writing these instructions based on how I think will work without wiping out the WUs. However, to be safe, wait until you have no running tasks.
1) Download the optimized client from Alex from »tbp.berkeley.edu/~alexka ··· ?C=M;O=D
2) Shutdown BOINC Manager
3) Copy all the files extracted from the archive to /Library/Application Support/BOINC Data/projects/setiathome.berkeley.edu"
4) Reinstall the BOINC manager from Berkeley (this is important, it resets the permissions of files in the project directory)
5) Restart BOINC Manager and in the messages you should see "app_info.xml found, using anonymous platform".
6) Watch your work time plummet.