This post :
shows that you cannot normally get to the CLI from within Raspbmc, however, this particular post
seems to show that it can be done using python.
sudo apt-get install python-dev <--Installs the Python development?
sudo apt-get install python-pip <--Python package installer
then create a file, that contains python script:
subprocess.call("sudo /etc/init.d/transmission-daemon start", shell=True)
and last, assign this script to a button on remote:
I suppose that this gets you to the CLI where you can do your keyboard magic