Using multiple .dir-locals.el

Question

Say I have two directories A and B, with A containing B. Both A and B have directory local variables specified through their own .dir-locals.el files. B/.dir-locals.el whenever emacs visits a file in B. However, I want emacs to load B/.dir-locals.el and A/.dir-locals.el. Is there a way to customize this behaviour? If not, how do I achieve this behaviour?