On-Demand Icecast streaming

[H.Wade Minter]

I'm trying to set up something for a client on our FreeBSD 4.8 
machines, and am stumped as to how to get it to work.  Hopefully 
someone here will have an idea.

The client has a bunch of audio recaps in MP3 format.  They want 
someone to be able to come to their website, click on a link, and have 
one of those recaps streamed to them.  This should be possible for an 
arbitrary number of people, each listening to the same or different 
streams.

I've grabbed icecast and shout from the ports tree, but can't wrap my 
brain around how I'd implement the on-demand streaming.  Most 
documentation I've seen is written around web radio streaming, where 
you have a fixed playlist and an arbitrary number of clients listening 
to the same thing, which doesn't fit what I need.

Anyone have any hints?

--Wade