[OpenSIPS-Users] OpenSIPs acting as a SIP router only

[Soul Reaper]

I have just finished installing OpenSIPs about an hour ago. I have gone through the cookbook available but  didn't find any elaboration on Source IP rewriting. Before even I start to confuse myself let me explain exactly what I want to achieve with OpenSIPs. I have Asterisk and A2Billing setup properly and they are working fine. OpenSIPs is also installed properly and both are listening on all IPs of the host. I want to use OpenSIPs as a SIP router such that I can send calls and REGISTER to the same host via independent IP addresses. The IPs will be assigned on the basis of the username in the SIP URI. The host has six IPs and all are Public. Can anyone suggest or guide me in the right direction about what module-specific parameters to use or how to use them and a starter script for the routing logic specific to changing source IP. Users will always be behind asterisk and Asterisk will connect to trunks via OpenSIPs. Thank you