Ah yes, this took me a while to figure out the best way to accomplish.
What I used to do is temporarily turn tabbing off, then have the windows floating, transfer the layers, then turn tabbing back on. I could keep tabbing off permanently, but I like what it looks like.
However, I only just recently found the "Arrange Documents" button found here:
Just select "2 Up" and transfer your layers, then switch back!