While the motion of a classical particle bounded to a surface depends only on the local curvature, the dynamics of a quantum particle depends also on the mean surface curvature. Its influence can be experimentally observed using surface plasmon polaritons (SPPs), which are naturally surface-bounded waves. Owing to the similarity between the Schrödinger and the paraxial Helmholtz equations, this system can be used to readily examine quantum phenomena. In this work, we experimentally show a new guiding mechanism based on this quantum effect using the surface curvature of a book-cover structure, whereas in the case of an inverse book cover with the same local curvature but inverted mean curvature, the SPPs rapidly diffract. Additionally we show that, by longitudinally bending the book cover, the propagating mode width can be dynamically controlled.