MP3 player - Stereo socket with switch for power anywhere?

Hi,

I'm attempting to get an Archos MP3 jukbox connected as a plug-in
jukebox in my car. My problem is I'm using an RF modulator to convert
the line-in signal to the radio input (which works fine by the way),
but the RF modulator wipes out all other radio signals when its
powered on.

My question is therfore.... Is there a 3.5mm stereo jack socket
available with a built-in switch that will connect the 12V to the RF
modulator when a plug is inserted into the socket (I know I could use
a separate switch here but I'm a bit of a perfectionist so I'd rather
not do this).

Any info appreciated