[SR-Users] URI Mapping in Presence?

Hi All Looking for the best way to achieve mapping from requested uri to actual uri in presence subscription. The scenario I’ve been presented with is that there is a direct relation between extension number and sip user but they are not the same thing. So for example; Extension 10 is mapped to SIP user sip-SomethingLong Extension 11 is mapped to SIP user sip-SomethingEvenLonger When extension 10 subscribes to 11 we end up with something like this; From: “Extension 10" <sip:sip-SomethingLong@ourpbx.com:5060>;tag=12345678 To: <sip:11@ourpbx.com:5060>;tag=987654321-c8bd I *think* what I need to end up with in presence db is; presently_uri = sip:sip-SomethingEvenLonger@ourpbx.com to_user = 10 (Is that right?) However I can’t see a standard way to achieve this. Manage_subscribe will let me override the watcher uri but not the watched. Anyone see a simple way to achieve this? Thanks Mark