If my blocks are going to be separated by sashing, anyway, I avoid having to hand stitch anything by attaching the backing of the blocks to each other. After trimming the batting to lay flat, I sew the sashing onto the front using one of the 8 gazillion methods available. With narrow sashing ... say an inch or so ... there's nothing else to do. If the sashing is wider than 1.5 inches, I do a bit of quilting down the middle to make sure the batting stays flat.
Because I can be a bit of a clutz, I sometimes use an ultra-light weight double-sided fusing material to secure the sashing to the blocks, then topstitch down each side. That way I know the sashes will be properly centered and straight.