From Roderich Schupp I received the following instructions:

cp /usr/share/doc/hal/examples/10-x11-input.fdi /etc/hal/fdi/policy/

And in order to set a default keymap:

<deviceinfo version="0.2">
  <device>
    <match key="input.xkb.rules" contains="base">
      <merge key="input.xkb.layout" type="string">de</merge>
      <merge key="input.xkb.variant" type="string">nodeadkeys</merge>
    </match>
  </device>
</deviceinfo>

Into yet another custom file in this directory.

Thank you, I’m going to try that on my next reboot (which may take a week).