You could get a pencil and some blu-tack...
If you stuck the blu-tack over the cursor keys and whacked the pencil in the middle - hey presto!
Instant joystick.
[ed]
I just tried it out, and you need something to strut the axis with. I used matches, but I'm sure anything like that would do... You also need an elastic band, wrapped round a lot of times, in order for the struts to be solid enough to press the keys when pressure is applied to the pencil.
Paperclips would probably be best, actually.
