I'm pretty sure there is no way to configure the network settings on a Slingbox without going through the setup assistant.
Once you've configured a Slingbox with a static IP and such that cooperates with your network, it should retain those settings unless you do a hard reset... no weird DHCP circus to contend with after that.
If having a quick and direct way to set those parameters is enough to do what you need, I'd suggest taking a laptop with you, connecting directly to each Slingbox via ethernet one at a time and run the setup assistant like that. After you've updated the network settings, reboot the Slingbox (power cycle, not reset) and plug it back into the router.
The easiest way to do this would be from a Mac because of the way its version of SlingPlayer works. If someone has a Mac laptop handy (even an old one- anything with a G4 and Mac OS X 10.3 or better), grab it and download a copy of the Mac SlingPlayer (direct link for the disk image). It's completely standalone, no dependencies on Sling Accounts or the cloud-based Directory, and the config utility doesn't require an active internet connection. Plus, the utilities are separate- you don't need to run through the whole gamut of wizards if you don't want to, just the one for network settings:
It'll take less than 90 seconds to configure the IP, subnet mask, gateway and port for each Slingbox... and that includes the time required to fiddle with the ethernet cable.
If there aren't any Macs handy, I'm fairly certain you can do it from the Windows SlingPlayer too (link to download page). The current version relies on the cloud-based Directory quite a bit, but I think you can pull this off without an active internet connection or Sling account. If not, dig around for an older (pre-2.0) version of the Win SlingPlayer that was released before Sling Accounts were integrated. If you find a copy, everything should work about the same as I just described for the Mac.
So... unless you've got a gob of Slingboxes and physical access is an issue-- or I've missed the boat entirely on what you need-- I think this is the quickest, most efficient way to get your stuff configured.
Hope this helps,
The root of your question can be answered above by setting static ip address and letting your network administrator the TCP it uses to communicate.
When you setup the internet viewing, it then changes IP to the upper end of the subnet and sets the Default gateway from the dhcp server while waiting for you to set a static IP. You have to change NATs on the FWs and keep an eye on the mac address in the arp table for the changing IP address. As I said...Kinda complicated in a corp environment.
Your DHCP server will have a range of ip address for a given subnet. It will also have a default gatway assignment if your subnet is connected to another network. The default gateway is usually a router or layer 3 switch. This is the device that will route packets outside of your subnet. When you turn on your Slingbox, it will send a DHCP broadcast requesting its network configuration from your DHCP server. Your DHCP will then assign the network configuration to your Slingbox.
When you setup your Slingbox for internet viewing, it cannot "change to the upper end of the subnet" and doesn't "change gateways while waiting for a static ip". However as a Universal Plug and Play (uPnP) device it will attempt to send information to your router. If your router is uPnP enabled then it will attempt to set up the respective firewall rules to allow external access. This is because it requires to communicate using a specific TCP port from your internet gateway. This works fine in most residential configuration since its usually just one gateway away from the internet.
Once it establishes a valid route to the internet, it will then attempt to register itself to dish.sling.com. This is acts sort of a dynamic dns directory, which allows you to connect to your slingbox without knowning the external IP address of your network assigned by your ISP. This is important since most residential ISPs don't assign a static IP address.
However in a corporate enviroment, you might need to jump through a couple of gateways or even access a proxy server to get out to the internet. And I think that's where you might be a little confused in your understanding. In all honesty, if your network administrators are worth their pay, you can just tell them your Slingbox's MAC address and they will be able to set up the routes and firewall rules necessary to access your Slingbox from another subnet or the internet.
Basically, once your Slingbox obtains an DHCP IP address, you can
1. Use Slingplayer to configure a static IP address and change TCP port using the Setup Assistant
2. Get the Slingbox's MAC information from the SlingPlayer command line | Help | About Slingbox (Alt + E) | Informaton Tab