I have a machine with disabled ethernet and wifi because of drivers...
The method I use (and am about to use again) is to find the url of the file it's attempting to download and download it using a different machine, then I copy the file back over using a usb stick and place it in the cache directory for installation.
Full instructions:
sudo apt-get install foo
or
sudo jockey
or
wget foo
With the wget instruction you can just copy the url without running the command, for the others you should attempt the copy the urls from the output. If it helps, save them to a text file on your usb stick.
You can use wget or firefox to download the urls on a working machine:
wget http://foo.foo.com/foo.deb
Then save them all to a usb stick and place on the target machine:
sudo cp /media/MyUSBStick/*.deb /var/cache/apt/archives/
When you run the apt-get or jockey command again, it should then just use the archived version.
I understand that these instructions are not explicit, though I'm hoping you get the idea enough to be able to install whatever you need when ever you have a machine without an internet connection.