Batch/image process done scripts

I ran into the script to play a sound when a capture comes in, and would like to do a version of it that plays a sound when the batch process queue completes. Changing the 'on CO_CaptureDone' to something like 'on CO_BatchDone' seems like the right thing to do given what's in the CO AppleScript Dictionary, but this doesn't seem to work. Do I need to register the script using 'set batch done script' instead? Can there be multiple batch-done scripts, and if so, how does one control how they get chained?

Is there a reference for this around anywhere?