But there might be a way for GSX to read the passenger number variable direct from FSCaptain.
The people at FSCaptain have always been VERY supportive for further interactions with GSX and adjusted parts of their program to read GSX L variables.
We already documented all the ( two ) required variables, in the most recent version of the GSX manual, and they are already working in the current GSX version, just with a simulated number of passenger, but it's more than enough for any developer to add support for this in his code and test it and, the moment we'll release the expansion, the simulated number will be replaced with actual animated passengers.