IAX2 trunk - override outbound Caller ID

Hi all,

It's the first time that I'm linking two Trixboxes using an IAX2 trunk. Everything works fine, but I've one thing missing that I don't even know if it's possible to accomplish. My setup is very easy:

* Location1: One trixbox 2.6.1 in the main office, with a PRI and a bunch of sip extensions (this one has been working flawlessly for more than a year and a half). Extensions 3XX
* Location2: One Trixbox 2.8.03 in the new office, with just 50 SIP extensions and a IAX2 Trunk to Location one. Extensions 5XX

I can make calls between 3XX and 5XX and also place calls to the outside world using the PRI in Location1 from both places. But, and here comes the question, is it possible to make calls placed FROM Location2 (5XX) have a different CallerID?

We have an IVR for each office (it's not possible to have just one for both) and I'd like calls placed from Location1 to present the DID assigned to the IVR, so people can know who's calling. I don't know if I managed to explain myself, but I've thinking about this for a while and I'm not able to find out the solution.

Thank you very much in advance.

BR,
\Ignacio.