Max Anstötz, that's what I thinking of trying. I read a methods paper where multiple brains were hemisected and embedded in an OCT block. I'm going to try what you suggested and see how that goes.
I understand your problem. Then you can go with Maxs` suggestion. But if you use adult rat brains, you can only cut three of them because of the length of the blade at the vibratome. So it still needs a little bit of room at the sides to swing correctly.