We use a live stream when a DJ is not online.  We would like our DJs to be able to have priority over that stream so they don't have to go to the server shut down the stream then start their's then hopefully remember to go back and start up the live stream.

This is already possible by using DJ accounts for Shoutcast v2:
http://www.centova.com/doc/cast/user_manual/01_usage_guide/02_advanced_usage/03_Providing_Access_to_DJs

And for Icecast the procedure is documented here:
http://www.centova.com/en/faq/general/information/how_does_the_automatic_live_autodj_switching_feature_for_icecast