storm at sea

I'm thinking of Storm at Sea. Specifically, I'm thinking of the diamond
in a rectangle unit that goes into the storm at sea block. Is there a
clever easy way of piecing this? I've used templates, but templates are
a pain. I've paper pieced it, but that wastes a lot of fabric, and I
suspect there's an easier way, something that's dopeslappingly obvious
after someone points it out to you and accurate to boot. I'm hoping
maybe for a ruler made specifically for the unit and instructions that
go with it.

--Lia