You have 2 options. Use a reflector so it's a URL that can be reached from anywhere, or if using the Mac app too use the Home Remote: Remote functionality (looks like a double ended arrow in the iOS app). This will relay local commands from your iOS app to the Mac app which will then call them.
Home Remote: Remote uses an SSID list to know when you are at home. When at home it will just call from your device, when on a different network it will relay to the other clients.