Hi,
The security deposit is the landlord want to make sure that you won't demage anything at their house. What I will say, you may let your landlord know your situation and hope they will let you to pay the deposit slightly later.
If your landlord is Chinese, probably they want to have a good tenant and expat for them is a type of good one. Just try that first and see what will happen. If the landlord refuse to do that you might need to rent the service apartment. In Hong Kong there are few hotel have that kind of service. For example, Harbour Plaza, Horizon...etc.
Or you can pm me which area you would like to live and let me try to help you.
Hebe