I'm not an Aussie, but isn't this worry about the lack of alternates for PER a bit misplaced? Due to prevailing winds from west to east, I would expect the block time from LHR to PER to be at least an hour shorter than PER to LHR. Therefore, if the latter flight is feasible, the former should be able to have at least an extra hour of fuel to divert to a more distant alternate.