I found some info on the net, the best of which appeared to be this one;
Mycila Blog: Reverse USB Tethering with Android 2.2
Also, with my WiFi turned off I selected one or two apps to be installed. Later when I turned the WiFi on the apps were downloaded and installed. So if push comes to shove, when you go somewhere that does have a WiFi connection you can install, I don`t know if this is time limited though. Another way is to get the .APK files and use and .APK installer App to install them. Astro File Manager may be a good idea to use too, as well as the installer itself.
For me I`d just add a WiFi adaptor and lock access to the network to named Mac Addresses only. But if that`s a route you don`t want to go down then I understand. It just means a bit more work and research to make it happen, because these things are tailored to WiFi use in the main.