The only way that slalom type racing can happen in winter is on a last minute go with the forecast approach.
If you want it to happen post here on a suitable forecast and we will see what we can do.
Also if you have a GPS why not just issue a challenge to your mates. Fastest alpha of the day. Side by side Nautical mile drag. 1 Hr challenge. Fastest across the river. Just use software to find out the winner.
Remember WWA has GPS units for loan to members. PM me or send an e-mail through info at windsurfingwa dot org.au if you are interested or need help with ideas.