Air Hong Kong (the A300 freight mob) is based in HK but the crews are Singapore based to avoid the higher costs of HK, however I believe crews can request HK as a base but remain on the same COS.
There are ways around it and if the number of cadets applicants to CX from overseas knowing full well that they won't get expat housing is any sign, those with shiny jet syndrome or a quick command will fill the slots.
