I admit I have no experience with transferring points, so what I will say is just based on reading HH T&C
A new Hilton Honors Member can pool, transfer, or receive Points 30 days after enrollment providing they have activity on their account. After 90 days of enrollment, a new Member is eligible to pool, transfer, or receive Points regardless of their account activity.
The morale here: Ask your friend to book a cheap 1-night stay at a low-end Hilton property somewhere around. Once this posts, the 30-day condition becomes valid, and thus transfers become available in both directions. The same applies when purchasing points as well:
A new Hilton Honors Member may purchase Points 30 days after enrollment if the account reflects activity including a stay or earning Hilton Honors Points through a Hilton Hilton Honors Marketing Partner. After 90 days of enrollment, a new Member is eligible to purchase Points regardless of their account activity.
I see another possible obstacle though: as long as the account is "new" (i.e. prior to the expiration of 30 / 90 days), it may be the case that it will also not be possible to receive the points from AmEx, you need to verify that with HH (unless you are 100% certain).
Obviously, given the uncertainty with availability, if the AmEx points are transferrable, it is best to book 3 Reward Nights + 2 Cash Nights at a flexible rate (which will be high, but no payment will be due, normally up until around arrival). Once all 480k points are available and availability is hopefully still there, just cancel the above two and book as originally intended.
Alternatively, as you are aware, one can book a reward stay on behalf of someone else, and especially with a honeymoon stay this cannot be any issue (nevertheless, out of caution, I would definitely write to the hotel as well). If you have 480k points available, you can book the stay for the couple - just make sure their names are included as guests in the reservation - and your friend can subsequently transfer the points back to you, once this is possible. Just beware the below restriction (if you regularly make points transfers):
Each Hilton Honors Member is limited to sending no more than five hundred thousand (500,000) Points and receiving two million (2,000,000) Points via Points Pooling or Transfers combined per calendar year. Each Hilton Honors Member is limited to making six (6) transfers to other member accounts and six (6) Hilton Points Pooling transactions per calendar year.
I hope you are able to find a solution that works.