Catch the GSX menue with a LUA script and write it to a file. I use the vb.net filesystemwatcher to get triggered if the file content changes. Then I read the file and perform accordingly via the FSUIPC Client DLL for .NET, by Paul Henty. This is not very straight forward, but the only possibilty I see for a 'full' integration' of GSX into a flight deck environment. With adapted timing the GSX menus appear not longer than the blink of an eye. I control the complete boarding process in this way, based on the flight plan depature time (Simbrief, data.xml). Catering, boarding process, etc. are triggered in a timely manner, with the goal that the aircraft can block-off on-time. Number of passengers, boarding via jetway / apron position, deicing (if required), and more are taken into account.
Ruediger