Further to my post about portable apps, you might be able to install Silverlight on a personal machine and then drag the files over into the appropriate folder on your PortableApps version of Firefox:
http://portableapps.com/node/14188 (scroll all the way down to the last post)
I can't test it right now because, well, I AM the IT guy and yes, Silverlight is installed and I am watching curling.
