Spitfire plugins are typically automated through the use of MIDI CC. In Reason however, MIDI CC is not available in the automation lanes, but the parameters of the plugins can still be automated.
To start, you'll want to enable "Edit Mode" for the plugin that you wish to automate. In this case, I'll be doing so for an instance of BBC SO Discover.
From there, you'll need to click the very small and last icon underneath the zoom controls. This is where you'll find a pop out menu that allows access to the available automation lanes.
Now, hover over Group 1 or 2 to access the various parameters that can be automated. These will correspond directly with the plugin, so you should see controls such as Expression and Dynamics. Clicking on the name of a parameter will then add it in the form of an automation lane below the piano roll.
Another method of doing this directly from the plugin window is by clicking "Automate" at the top of the plugin window and then selecting a parameter. An automation lane that corresponds to the clicked on parameter will then appear in the piano roll view.
