I managed to get it running as I wished. The only thing, that I couldn't
solve in a nice way was using fluxbox instead of Xfce upon login in xdm, but
a little hack did the trick.
I left my setup as described and added an init-script /etc/init.d/xdm2 which
is mostly copy and paste from /etc/init.d/xdm trimmed down to what I
actually need. It simply starts xdm, which does the Right Things(tm) after
configuration. I edited /etc/X11/xdm/Xservers to account for the allready
running X. Then I hacked /etc/X11/xdm/xdm-config to point to fluxbox in a
That's it. Works fine
Aoccdrnig to a threoy, it deosn't mttaer in waht oredr the ltteers in a wrod
are, the olny iprmoatnt tihng is taht the frist and lsat ltteer are in the
rghit pclae. The rset can be a taotl mses and you can sitll raed it in msot
csaes. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef,
but the wrod as a wlohe. And I awlyas thought slpeling was ipmorantt.