Accessing quark GPDs in diffractive events at an electron-ion collider

We discuss two collider processes which combine a diffractively produced $rho$ meson separated by a large rapidity gap from a hard exclusive scattering of a Pomeron on a nucleon, giving rise to a lepton pair or to a second meson. These two processes probe the nucleon quark content described by generalized parton distributions in a very specific way.