Mi sono risolto la "finezza" da solo come immaginavo ho modificato il file 40compositing-vm

#!/bin/sh
# to be sourced

if [ -r ~/.compositing-wm ]; then
  CONFIG=~/.compositing-wm
else
  CONFIG=/etc/sysconfig/compositing-wm
fi

COMPOSITING_WM=`sh -c "source $CONFIG; echo \\$COMPOSITING_WM"`
if [ -z "$COMPOSITING_WM" ]; then
  COMPOSITING_WM=compiz
  unset CONFIG
fi

# read package defaults first
WM_CONFIG=/usr/share/compositing-wm/$COMPOSITING_WM.defaults
[ -r "$WM_CONFIG" ] && . $WM_CONFIG

# allow system defaults to override package defaults
[ -r "$CONFIG" ] && . $CONFIG

[ "$SESSION" = "failsafe" -o "$SESSION" = "drak3d" ] && COMPOSITING_WM_START=no

if [ "$COMPOSITING_WM_START" = "auto" ]; then
  # auto-start composting window manager if Xgl is started
  # or if direct rendering and GLX_EXT_texture_from_pixmap are available
  source /etc/init.d/functions
  if grep -q no3ddesktop /proc/cmdline; then
    COMPOSITING_WM_START=no
  elif [ "$XGL" = "yes" ]; then
    COMPOSITING_WM_START=yes
  elif glxinfo 2>/dev/null | awk 'BEGIN { no_direct = 1; no_tfp = 1 } /direct rendering: Yes/ { no_direct = 0 } /GLX_EXT_texture_from_pixmap/ { no_tfp = 0 } END { exit or(no_direct, no_tfp) }'; then
    COMPOSITING_WM_START=yes
  else
    COMPOSITING_WM_START=no
  fi
fi

export COMPOSITING_WM_START
if [ "$COMPOSITING_WM_START" = "yes" ]; then
  START=/usr/bin/compositing-wm-start
  case "$SESSION" in
    GNOME)
      export WINDOW_MANAGER=$START
      ;;
    KDE3)
      export KDEWM=$START
      ;;
    KDE4)
      if [ "$COMPOSITING_WM" = "compiz" -o "$COMPOSITING_WM" = "compiz-fusion" ]; then
          export KDEWM=kwin #$COMPOSITING_WM (questa è la riga modificata)
      else
          export KDEWM=$START
      fi
      ;;
    *)
      $START
      ;;
  esac
    
  # Start the decorator now to allow compiz to be saved into session
  if [ -n "$COMPOSITING_WINDOW_DECORATOR" ]; then
    $COMPOSITING_WINDOW_DECORATOR &
  fi
fi

Ora gnome parte di default con compiz e kde parte di default con kwin senza cambi di windows manager e senza bisogno di fusion-icon