each person's family would have an opportunity to put a lei onto the memorial grounds

Talking of remembering with flowers:

GREAT BRITAIN

Three thousand white rose petals were released from the Whispering Gallery in St Paul's Cathedral. The petals represented all of those who lost their lives in New York, Washington and Pennsylvania.


from: http://makeashorterlink.com/?K160517C1

I caught this on the BBC News, and it was really beautiful - petals descending like snow, each one standing for a life.
After the service many people (including relatives of victims) spontaneously went to pick up petals to take away with them. Very moving.