Regaring his plan, I don't know it at all.
=Concerning his plan, ---
=Respecting his plan, ---
=Touching his plan, ---
=As for his plan, ---
With regard to his plan, ---
That's what the grammar book said. (eye-rolling)
And I would avoid making friends with 'touching' because it is just my nodding acquaintance unless you teach me how to use it.