Is it possible to queue up multiple message to go to the same device?
No, you can only queue one message
at a time for a particular endpoint. Each endpoint has its own queue
that is independent of the others. The purpose of the queued message is
to immediately send a message to a sleepy endpoint when it has waken up
and reported back to the coordinator. There is a period of time defined
by the Listen Window parameter that determines how long the endpoint
will wait for a message before it goes back to sleep. The queue feature
allows a message to be sent immediately after an endpoint reports in
with a supervisory message which minimizes the necessary listen window
and thus maximizes battery life.