It looks like you will actually need 2 blocks with individual sashings. (I've not given sizes here, just a diagram of how to sash.)
One block is sashed all around it.
Another block will be sashed on only 2 sides WITHOUT the cornerstones.
A third block will be unsashed (plain).
The first two blocks will form one row. The next row will require you to turn the partially sashed block on its side, then use a plain unsashed block beside it to complete the row.
Jan in VA