Not sure if this is a good idea.

So, here are the pieces for the desktop as they will soon go together.  It looks pretty straightforward, but there's a rub.  My son was absolutely adamant that the rear part of the top and the gallery be quickly and easily removable because he expects to change apartments frequently.  I argued against it strenuously to no avail.  What that means is that there will be a seam across the desktop right in front of the gallery that will be prominent in the middle of the desk where the top extends all the way to the back.  Yuk.  What I decided to do is use hardware made for table leaves to hold the two pieces of the top together.  The front of the top will be held in place like a normal top and the rear portion with the gallery will come off.  The expansion and contraction will happen toward the back.  Using the Woodweb calculator, the expected expansion is less than half an inch, the value for flatsawn lumber, and more than a quarter of an inch, the value for radial sawn lumber.

The first thing I did was carefully joint the two pieces of the top face to face.  By the way, that's Maude in the picture below, with her painted knob and tote and bakelite adjuster carefully stowed away in a drawer, replaced by rosewood, brass and a Hock blade and chipbreaker.  As usual, Maude worked great.  

Then I installed the hardware, two latches on the sides that pull the pieces together and two positioners (I don't know what else to call them) in the middle that fix the position of the "leaves" side to side and up and down.

 

 With a lot of trepidation, I turned it over and it wasn't too bad.  This is a close-up shot of the center that I am most concerned about.  Surprisingly, it is smooth to the touch.  It looks like, well, it looks like a dining room table with a leaf in it.  Big surprise.

 I don't like this, but it was the best way I could think of to do what he wants.  Another way that occurred to me as I was doing it is to glue blocks onto the bottoms of the pieces at the joint line and fasten them together with bolts.  It would have taken longer to take the top apart but would perhaps have been a little more secure.  Oh well.

The remaining task is to come up with a way to fasten the gallery to the rear stretcher that will allow it to be removed quickly.  He will need to be able to undo the latches and slide the gallery back in order to disengage the positioners before lifting the gallery up.  That means the attachments in the back will have to accommodate a considerable amount of movement.  I've got a strange idea that I think will work.