SIP trunk using Milkfish (proxy)

Hello

My asterisk system is sitting behind an ADSL router and I would like to route my SIP trunks via the Milkfish Proxy (embedded in my dd-wrt router). This is preferred to range port forwarding.

I have looked at the configuration options of the SIP trunk and cannot see how I would define this.

Can SIP trunks utilise a SIP proxy ?

Thanks…Pete