No real good way to do this. I had a car dealership that wanted to know when someone was calling in on the 800 number with a different ring tone. I just created a non billable line with an extension. Then I programmed that line key on all the phones that needed to ring when the 800 number was called. I then set each phone to have a different ring tine for that line on the individual phones.
In you case, maybe you can create an overflow ring group / call queue that rings the newly created extension. Each phone will have the line key programmed on it and then you can set a distinctive ring tone on each phone.
Hope that helps.
