This idea pops up every now and then when people are frustrated with the freight company's.
I bought a board back from Brisbane a couple of months ago.
www.seabreeze.com.au/forums/Windsurfing/Queensland/Brisbane-Freight-Co-recommendations?page=1#lastpostNo problems for me as had room and the buyer was not in a hurry. ( Evan picked the board up from the seller ). Did not expect any payment as I knew both seller and buyer, but did receive some liquid refreshments

This thread would need to keep active to work.
Just post dates of when you are travelling from and destination. What they have room for e.g. board / sail/ boom etc.
A bit more difficult from East Coast to West Oz but doable especially over summer months and there were no time constraints. Could even involve two different stages e.g. Sydney to Lake George then Lake George to Perth when heading home.