Hi there
It is a commonly extended courtesy to route Victor flights)of all States)as near direct as possible, even if it means going off airways. The same also applies to State air ambulance or rescue flights, for obvious reasons. Also, the State does recieve a bill for ATC services but it is dealt with at State level; ie, the Dept of Finance will pay once a year and so on. States don't tend to charge each other for the passage and servicing of State aircraft.....The Dept of Foreign Affairs are the real controllers of the VIP aircraft and decide what their tasks will be.The Don does what it's told.
regards
GttC