Apparently (rumour network!) the SY VOR and DME will be decommissioned once all six ILS's at Sydney have discrete DME frequencies. Then the problem will go away.
In any case, I find it helpful to remember that the sole purpose of a DME on an ILS is to provide a glideslope integrity check. Which particular navigation device is used to achieve this goal is unimportant. Could even use the GPS, if national law permitted it.