[SR-Users] Add CallerID to SIP header

I'm not yet using Kamailio. I am looking for something to do a job which sounds really simple but may not be. Our PBX connects to a SIP service (voicetrading.com) but does not supply our CallerID, this means that voicetrading.com provide some very weird callerids for the person at the other end (international numbers etc). Which is not good. There is no way to get our PBX to add CallerID itself, so I thought maybe I could set up a local sip proxy? or sip redirect? server (Kamailio?) to do nothing other than add in the callerid details to the sip header and then forward the sip message on to voicetrading i.e. be otherwise 'invisible'? If Kamailio is not the right thing to do this with, is there something else that could do it? Thanks for any suggestions. Dominic