Thanks Hilmar.
After digging into the API code and seeing how the messages were handled I realised the answer to my question was "NO" it is not possible. Also, as you mention, checking/clearing the message deque would not be sufficient if the messages hadn't even arrived yet.
I have modified my model to cater for such "late" data and so far so good. It meant adding a mutex around the display buffer (separating updates from clearing) which might impact code speed but doesn't really matter since this is all user interface stuff.
