If he's not looking to start a business employing local people then it's not at all easy (otherwise everyone wanting to just come and stay here would claim to be a "consultant"). If he would be employing local people then he could try getting an Investment Visa, which will require him to have a business plan and so on. See section 15 on page 3 of
this document and page 4 of
this document for the sort of paperwork required.
The other option if he has HK$6.5M is the
Capital Investment Entrant Scheme.
