This is now implemented: Install modified-hildon-desktop from here. Run in X-Term the command Code: gconftool-2 -s /apps/osso/hildon-desktop/key-actions/ctrl_backspace_in_tasknav -t int 3 See here for more options of this program.
gconftool-2 -s /apps/osso/hildon-desktop/key-actions/ctrl_backspace_in_tasknav -t int 3