Based on my last visit to the airport, departing duty free shops in HK will not sell alcohol to you if you hold a U.S. bound boarding pass.

I'm not sure I agree with ssw207's statement that bringing liquor back to landside is an offence under the DGO, but it would be a massive headache (including missing your flight) if customs did randomly search you - they may not buy an explanation that you wanted to put it in your checked baggage.

Buying a fully refundable ticket, showing that boarding pass to the duty free shop, and then cancelling the ticket would also not work because of the gate check and a little old thing we call fraud.