I don't know if they could risk doing that without offering some significant compensation, remember that a lot of the pax will be OOL based FIFO people flying home at the end of their roster, you would expect quite a bit of pushback and/or a ruckus being kicked up at PER if that was the case.
With the headwinds and range limitations of the A320s - wouldn't it be flying the other way from OOL-PER that would have the fuel/load limitations associated with strong headwinds? Strong headwinds from the west would be limiting the A320 for the OOL to PER flights, in which case JQ could have problems trying to redirect offloaded passengers leaving OOL and going to PER. The best they could offer is flying the next day on JQ but that definately wouldn't cut the mustard for people who have to be in Perth to get connecting flights to work/mine sites.