You can seek to persuade political parties to allow voters who are not party members to have a say in the preselection of party candidates.
This is common in the US and UK, and has been done on occasions by all major parties in Australia. It’s sometimes called ‘community preselection’. There is no reason why it can’t be more common here, especially as it would be advantageous for parties to be endorsing a candidate who has been shown to be more popular than other contenders. The decision to allow this may need to be taken by parties at a state or national level, so you may need to conduct a coordinated campaign for it across electorates.
Here are some suggestions for making this happen: