Depends on the company... If a big corporate it tends to be quite formulaic on the relocation package element, so I'd suggest you try to detach the promotion from the relocation package. I.e. negotiate hard based on what would the role be paid in HKD and start from there.
For the formulaic bit... Usually a cost of living allowance (+ or -), which might be pro-rated to exclude the bit of your income a formula assumes you'd save or spend on housing in HK, a housing allowance, adjustment for different tax rates (again + or -), and then converted into the destination currency. After that your destination pay would probably be adjusted for FX fluctuations periodically, although the cost of living adjustment will normally give some degree of offset.
Destination country will be picking up the costs so you'll mainly be negotiating with cost centre owners over there.