I tried to add build-essential through the edit menu of synaptic, the running sudo apt-get install build-essential from the terminal. Unfortunately, it still tried to download from the internet.
In this application, there is no way to string a wired connection to the machine.
I decided to give Xubuntu a whirl, as I remember with Ubuntu that adding from the LiveCD was possible. I followed the same procedure as above, & when I ran sudo apt-get install build-essential from the terminal, build-essential was installed from the disk.
I would think that this is possible from Mint as well, but who knows...