After a bunch of head scratching I came up with this super low-tech new version.
Kevin,
In your "fold the seatback to make the front part of the sleeping platform" arrangement are those a second set of the top latches holding the top (rearward) end of the flopped seatback in place?
Are they in the way when using the rear seat in it's normal configuration?
How to you handle the lower seatback hinge? Is it quick to release? Is it secure enough when in "seat" mode?
Thanks,
mark