That's a bit of a tough one--are the desks easily moved by the kids? If so, although it takes a bit of time, they could be moved facing forward for that handwriting time, and back into sets of four when that time is over. (Used tennis balls slit to fit over chair and desk legs cut way down on noise.)
Another idea is to look for "moveable" seating ideas that can be used besides desks. Many of our teachers use laundry baskets for the kids to sit in during read to self or baskets next to each other for read to self time. They can be turned upside down and used as a fairly smooth surface for WW or writing in a journal. Nothing like carpet squares that can be stacked out of the way when not in use 
. Maybe even under the desks for spaces, if your kids can handle that. I'm sure others have some great ideas to share!!
