The answer is yes, but you do have to have a US taxpayer ID or social security number. Current laws require that for anyone entering into any sort of financial transactions in the USA. Social Security does have procedures for issuing numbers to those who are not resident, and not permitted to work in the USA, the cards however have an Over print
'NOT VALID FOR EMPLOYMENT'. You should probably contact the US consulate to see if there if there is a way to do it in Hong Kong. You may have to come to the USA. If you do, you just have to showup at a Social Security office with proof of ID. Because these numbers are required for any sort of financial transactions in the USA (and foreigner are allowed to borrow money, own stocks/bonds, have brokerage accounts and insurance policies, and these all need the tax payer information, there is no drama in obtaining one for tax purposes.
By contrast obtaining a TFN in Australia (equivalent to a US Social Security or Taxpayer ID) is extremely difficult for people without the right to work in Australia. So difficult that anyone who has a TFN is assumed to be able to work legally.