I'm not sure this is true. Well, the 529 account can only ever have a single beneficiary; that's true. But the beneficiary does not always need to be a U.S. citizen.
You need a SSN or Taxpayer ID for both the Account Owner and Beneficiary in order to open the account. While the primary account must have a permanent U.S. residence listed for mailing purposes, most program documents state that the account owner and beneficiary need to be U.S. citizens or residents. Requirements of residence also likely to vary by state. You can compare those requirements here by selecting the options under, "Eligibility."
The main issue here is that the 529 plan provider needs to be able to conduct AML (anti-money laundering) and monitor for fraud, which means they need to be able to verify the identity of plan stakeholders. This requires verifiable identification information. So while it may be challenging to open an account for a non-U.S. citizen living abroad, it's not impossible. If the future student does not have a tax ID or SSN today, jingcha (the OP) could open a 529 account with him or herself as the beneficiary for now, and change the beneficiary once the future student acquires the necessary identifications.
VP, Research & Development
This information does not constitute tax advice and is provided for informational purposes only. Please consult your tax advisor, financial advisor, local taxing authority, and/or plan provider or sponsor for more information.