So to answer your question, no there is no way to configure the broker to insert a timestamp. Nothing the in AMQP specification requires a message to know when it arrives at the broker and keep in mind that manually inserting the timestamp on the broker side will only represent when the message was received by the broker, not when it was published.
If you are hell-bent on doing this you could write your own RabbitMQ plugin to do this but I would not recommend doing this. Instead I would recommend forcing your producers to include the timestamp in their message properties.
Resources: