The simplest way to achieve this would be to gift-wrap (NIP-59) the event to each of the recipients.

You create your kind 31922 event, then wrap it in a kind 13 seal using the event creator's real key (encrypted via NIP-44 to the recipient). Next, you wrap that in a kind 1059 using a one-time key (nip-44 encrypted to the recipient, again), and finally tag it with the recipient's #p tag.

You would do this for each recepient of the event.