I understand that you'd prefer to have more direct control over your router's port forwarding rules. Unfortunately, there's currently no way to manually configure port forwarding with either the Slingbox 350 or 500. This was done to make the initial configuration easier, and to also allow the Slingbox to automatically "repair" its network configuration without user intervention.
Your only option right now would be to disable UPnP on your router, which should prevent the Slingbox from creating new rules, but may also impact other devices on your network.
Hope this helps!
The Slingbox Answers Forum Moderation Team
I have read this year that many computer security experts -- and now even the US Dept of Homeland Security -- are encouraging home users to disable UPnP on their routers and other devices because of bugs in many of these devices software that makes them susceptible to break-ins, remote takeover, etc.
Similar risks have been noted for the Wi-Fi Protected Setup (WPS) feature on most routers manufactured after 2007. While WPS is handy for initially installing devices like WiFi printers to one's home LAN, the recommendation is that WPS be disabled on the router immediately after the new device is connected, as connections to the router from remote locations can be easily hacked if WPS is left turned on.