Don't just disable the networking, break or remove the adapter. Then you have a machine that can only be interfaced with through the USB or other ports.
But how do you actually do that? You need to do it physically?
I've been using an offline wallet to sign for a while, but I just disabled network adapters. I figured it was kinda bullshit....
Not at all.
Say the machine is one of those that have a little slide switch on the side, for wireless on or off. Stages in disabling wireless are:
1) software disable
2) slide the switch
3) tape the switch over in the off position
4) glue the switch one position
5) take the slide switch out (requires removing the cover)
6) take the computer's wireless card out