Voicemail ligh on a distant phone

I am working on using Freepbx to act as a voicmail system for another Asterisk based system. The reason is that I have 6 of the other systems and the customer wants a centralized voicemail. SO far I have the two systems connected over an iax trunk. I have setup a Virtual extension that will mirror the other extensions in the network. I have setup an IVR that will allow extension dialing. So now I can use a direct dial number that will let me dial a virtual extension and since there is no real device the voicemail is offered. So here comes the next bit that I have no clue what to do. I would like to light a light on the real extensions. Is there a way to do this in a field in the extension programming. This would help a great deal

Thanks alot for any comments