Ann: Westpac announces $3.5 billion off-market share buy-back, page-372

According to this, the ATO does not have a crystal clear definition for a wash sale.

https://www.morningstar.com.au/learn/article/avoid-this-expensive-tax-time-mistake/168452

It's safe to buy the replacement shares BEFORE the buyback date as these shares are not eligible for the buyback participation and cannot be considered as part of a wash sale. One has to come up with the money before the cash from the sale returns.

Another choice for people who can trade option is to sell put deep in the money to guarantee assignment and lock it in at the current share price. Sell it at the expiration of a couple of months from the buyback date to be sure.

So, the idea of selling into the buyback then using the cash to buy back the shares quickly would be considered as a wash sale if ATO detects this. I doubt that ATO would care to check on individual investors with a small number of shares.