Hi Lou,
yes, you can. That's what git is all about :) Git even has something called "bare repo" where you save the hassle (and the space) for a working copy.
If you e.g had an USB drive, you could do an
git clone --bare
https://github.com/gnuradio/gnuradio.gitand then pulling from that on your not-networked machine:
/home/lou/my-working-dir$ git pull /media/usbdrive/gnuradio.git
When updating GNU Radio, instead of re-cloning you could just git fetch the newest branch.
However, I might assume that you're doing this because you have a machine that you only use for deployment, so you most probably wouldn't want to compile GNU Radio on that but actually wanted to just install it there. If getting an image of that machine is feasible, look into just reproducing that machine in a virtualization solution (e.g. Virtualbox) and just overwrite the filesystem image of the non-networked machine.