Your best bet would probably be to set up icecast-oddcast or nicecast or jamcast and broadcast via one of the radio presets.
For jamcast: http://forums.roku.com/viewtopic.php?t=7875&highlight=jamcast
for icecast or nicecast (depending on your OS): http://forums.roku.com/viewtopic.php?t=5283&postdays=0&postorder=asc&highlight=pandora&start=0 Look for Foxcat’s instructions for Windows, or mine (andyg) for Nicecast on a Mac.
I haven’t tried jamcast but I think it may be less fiddly than the other two.
cheers, andy