Using a pen-drive could work, but not the way you use it.
What you need is to treat the pen-drive as a remote. So basically you
make a bare repository on the pen-drive and push-pull from it. Git will
then manage everything.
In short, something like this:
# make repository in pen-drive:
$ cd /path/to/pen/drive
$ mkdir repo; cd repo; git init --bare
And in your repositories (both at home and work):
$ git remote add pendrive /path/to/pen/drive/repo
You can then start pushing to/pulling from
same way you would do any other remote.
Still, more appropriate would be to ask your company to not block ssh to
GitHub (Unless you shouldn't be doing these stuff at work, in which case,
well don't do them at work).