Ian,
Yes. In this picture I use a right end and top. I made the top flush, and put a -.75 (material thickness) top inset on the right end panel. This will allow the panels to overlap so that when you apply the mitre tool to the both pieces you get the result that you see in the pic below. I have also attached the .hsf file along with the mitre tooI used.
Note: When using the PE to create the mitre, you may need to flip the piece from front to back to get the desired result.
If this is not the answer you were looking for let me know.