Hi Bowey,
It isn't documented yet, but on the 'develop' branch of the Bpod_Gen2 repository in /Plugins/PsychToolboxVideoServer/ there's a class called 'PsychToolboxFrameServer' that can display single frames on a second monitor. Usage is described in comments at the top of the class file. To have the state machine change the current frame, you'd set up a soft code handler pointing to PsychToolboxFrameServer's showFrame() method, and have the state machine send a soft code in the state where you want the screen changed.
This class is new, and experimental. We may modify it significantly before release to include support for psychToolbox's drawing primitives - but for now, it may already be useful. Please let us know if you encounter issues!
-Josh