Some feedback from recent experience to clarify / confirm some of what has been said above:

DXB-HKG - F upgrades from J are eligible for chauffeur drive but you have to call to book.
HKG-BKK in J - eligible for chauffeur drive if part of an international ticket (i.e. DXB-HKG-BKK). Not eligible for chauffeur drive on an "intra-Asia" BKK-HKG or vv ticket.
Transit/Stopover at DXB in J / F - if your stay in Dubai is less than 24 hours, chauffeur drive is available but only if the fare rules of the ticket permit a stopover