I managed to get this working. The trick was understanding that the Mouse Pick action doesn't fire on a left click, which I erroneously thought. It just fires a ray from the mouse position at any time requested, regardless of the state of the mouse.
So what I did was on Left Button Down I transition to a new state, "Left Button Down". In that state I have three actions. In one action I get the mouse movement (Get Axis Vector with axis of Mouse X and Mouse Y) and store the magnitude in a float. In another action I use Float Changed to send a transition "Mouse Movement" if that float changes. The last action is Get Mouse Button Up and fires a transition "Left Mouse Up".
"Mouse Movement" transitions to another state "Pan With Mouse" where I handle my panning. "Left Mouse Up" transitions to a state "Mouse Up After Click" where I perform the Mouse Pick and carry on as normal from there.
So in a nutshell after I see the user has pressed the left mouse button down, I then look to see if he moved the mouse before he released the button. If he releases the button without moving the mouse, then I transition to a pick, and if he moved the mouse first, I transition to a pan.