Routing audio for alerts/ringtones?

I currently have a Bose Companion 5 speaker system hooked up to my computer. It unfortunately has the 'feature' of automatically muting itself when the computer goes to sleep, and does not automatically unmute as the computer wakes. As a result, FaceTime and other sound-based alerts do not make any noise unless I'm actively at my computer with the speakers manually turned on.

Is there a way of making these rings and alert noises go through the iMac's internal speakers while preserving the output to the Bose speakers? I was able to configure "sound effects," which just appears to be a small number of outdated system noises (I've only heard "Funk" as the error noise), and does not remedy this issue.