bump texture with other texture

I got a cube with a displacement on it.

But not a physical displacement via Displacement Modifier. I just routed an image texture into the Displacement Slot of the Material Output in the Node Editor.
Now I want a second image texture to align with the displacement. By using a displacement modifier to change the geometry it’s simple.

But I already got to many vertecies. So I want to bump the second image texture via the one I achieved the (fake-) displacement with. But I don’t get there. It always looks, like the second texture is floating above the mesh, without aligning to the displacement.

Does anybody know, how to bump an image texture with another image texture without using a displacement modifier? Thanks in advance,