Thanks, all! It sure helps to hear the stories.
ultramarina, I love the box idea.
HJA, we also respect his emotions and help him work through them. Now that we're used to it, it's quite easy to see that it's all perfectly real to him. I had to laugh when my in-laws just could not fathom why he was devastated about having to say goodbye to the goose. They must have asked why he was crying at least 10 times. It was like they just couldn't process the notion.
And yes, it's pretty easy to "Remember the Joy". He gives us plenty of reasons to smile as well, like when he talks about all the "life lessons" he has learned from a book we just finished reading, or when he starts explaining grammar rules and reading strategies to DS4.