Thanks for all the replies!
This is definatley a tricky one, currently the best two options are looking like the 3dconnexions SpaceNavigator or a Touchpad..
My only issue with a touchpad is the pointer always being on screen.. I've played around with RR and found I can use gestures on the touchpad for use without looking at the screen.
Is there any way to have the pointer only appear when the mouse is moving? and then auto hide once it isn't ?
If so it looks like this would be the best method for me!