I tweaked the demo app that Mitch includes with his interface box so that it is more conducive to Car use. It is not great but should work while we wait for the official plugin.
I have not actually tried it in the car, with a Sirius tuner, so I hope it works!
All that I ask is that you let me know how (if) it works for you!
To install, First
Install .NET 2.0, if not installed then unzip the attached file to a folder, I chose C:\Program Files\Flux Media. Then add the app as an external app, using the settings pictured, and add it as a button in CF.
Here is what it looks like when running (not on a PC with Sirius tuner attached):
It has been a little buggy showing up properly in CF. I have found that if I hit the off button, then reselect it from the CF menu, it behaves the second time (strange).