asterisk users - Oct 2010 - Getting last 2 Sip registrations of same user

Hi,

As we know when a user registers from some other place, his first
registration is discarded or updated to new one. i wan to know if
there is any method we can store his previous registration too. so
that we can call both of his last and current locations somewhat like
this

Dial(Sip/abc-last&Sip/abc-current)

I think this has to be done by modifying the asterisk source code. plz guide me.

Nasir Javaid
Axvoice Inc