Unfortunately it is somewhat about luck through winter. If you don't foil then you're pretty much just waiting for those frontal systems to come through at lucky bay.
If your schedule allows for it, and you're desperate, you've got to be there at the beach waiting for it, and rig up as soon as it looks like its starting. Rig for the gusts, not the lulls, because the lulls are generally not sailable on any size sail.
also, watch for the steady forecasts where it doesn't keep chopping and changing day to day. Much like the forecast for this weekend has occurred, they've had sunday looking good for the larger part of the week, so chances are we're going to get some good wind tomorrow. (No, don't quote me on it

)
last but not least, be prepared to get skunked plenty through winter. Winter sailing in Perth is for the desperados/keen/stupid among us. I generally have at least one day standing in my wetsuit in the rain, looking out at the wind not coming in, and slowly realising that i'm going to have to derig in the rain and head for home before i turn into an ice block.
hope this has helped