We update our method to search for the origins of ultra-high energy cosmic rays. First, we modify a model of the coherent component of the Galactic magnetic field by exploiting the existence of thread-like patterns in the arrival directions of ultra-high energy cosmic rays. This information is expected to complement our knowledge about the magnetic field by Faraday rotation and synchrotron emission measurements. Second, in a simultaneous fit to all cosmic rays considered we use this data-driven Galactic magnetic field model as a mass spectrometer and adapt the nuclear charges such that their extragalactic directions are concentrated in as few clusters as possible. During the fit, the nuclear charges are constrained by the individual energy and shower-depth measurements. We show in a simulated astrophysical scenario that source directions can be reconstructed even within a substantial isotropic background and in compliance with expected uncertainties of the knowledge of the Galactic magnetic field.