'Aux method.'

def _sources_as_evoked(self, evoked, add_channels):

    if (add_channels is not None):
        picks = [evoked.ch_names.index(k) for k in add_channels]
    else:
        picks = []
    sources = self._transform_evoked(evoked)
    if (len(picks) > 1):
        data = np.r_[(sources, evoked.data[picks])]
    else:
        data = sources
    out = evoked.copy()
    out.data = data
    self._export_info(out.info, evoked, add_channels)
    return out
