I think your question will probably be better answered in the Modeling Design forum.
As far as I know, any 3D gauges modeled into the VC or the regular visual model will need to have their code added to the visual model when you build it.
I don't have much knowledge of how to do this for FSX, but I do know that in CFS3 a simple needle gauge can be built using animation tags.
In FSX, I believe there is also a way to include more complex XML code into a modeled gauge but I don't know for sure on the process.