We propose a method to study the nature of exotic hadrons by determining the
wave function renormalization constant Z from lattice simulations. It is
shown that, instead of studying the volume-dependence of the spectrum, one may
investigate the dependence of the spectrum on the twisting angle, imposing
twisted boundary conditions on the fermion fields on the lattice. In certain
cases, e.g., the case of the DK bound state which is addressed in detail, it
is demonstrated that the partial twisting is equivalent to the full twisting up
to exponentially small corrections