Using sketched entities as assembly contraints?

I have sketched two center rectangles on two different parts that need to be aligned. They are not on the same surface nor will they be when assembled. There centers and edges will be aligned as both rectangles are the same size.

How do I align these rectangles without creating an axis in the center of each?

They both have center points but not axis.

I'm finding it challenging to assemble them.

Any ideas?

SolidworksAssemblies