Is there a way or a module to give me a R.A.P. +12 output that can plug into the factory monsoon stereo?

here is the situation:
2008 Solstice, Monsoon Stereo and OnStar
I am not replacing the head unit, amplifier, or speakers. all I want to do is add my Sirius Sportster 4 to my system. I have the hard wire power supply, but need a +12 source to power it when the radio is on.

Is there a module to do this, or somewher eelse I can grab R.A.P. +12 (the monsoon amp maybe?) all the other +12 sources go off as soon as the key is not in the "run" position - less than useful.