  The purified SASE (pSASE) undulator configuration recently proposed at SLAC
promises an increase in the output spectral density of XFELs. In this article
we study a straightforward implementation of this configuration for the soft
x-ray beamline at the European XFEL. A few undulator cells, resonant at a
subharmonic of the FEL radiation, are used in the middle of the exponential
regime to amplify the radiation, while simultaneously reducing the FEL
bandwidth. Based on start-to-end simulations, we show that with the proposed
configuration the spectral density in the photon energy range between 1.3 keV
and 3 keV can be enhanced of an order of magnitude compared to the baseline
mode of operation. This option can be implemented into the tunable-gap SASE3
baseline undulator without additional hardware, and it is complementary to the
self-seeding option with grating monochromator proposed for the same undulator
line, which can cover the photon energy range between about 0.26 keV and 1 keV.
