  The end-point contributions in the quark longitudinal momentum fraction of
the virtual photon ($\gamma^*$) to vector meson ($V$) impact factor to the
diffractive electroproduction amplitude can be factorized in terms of a
generalized parton evolution of the target parton distribution. The result is
used to model the helicity amplitudes $\gamma^* p \to V p$ in terms of small
$x$ generalized parton distributions.
