I haven't tried it, but this sounds great.
The Toilet Tank Traffic Shaper - DUMMYNET rocks.
Is there something similar for PF? For Linux?
In vaguely related news I haven't had time to setup the Soekris box yet. My excuse is that I need to either work with OpenBSD or wait for FreeBSD to import the if_bridge code into 5.x to make it work well as a bridge.