Currently we don't have support for this. We added your request on our TODO list and hopefully such an improvement will be available in a future version of Advanced Installer. Thank you for your suggestion.
Our development team investigated this scenario and it seems you can write to the MSI installation log by simply using the "Write-Output" cmdlet into your PowerShell custom action code.
Hope this is still valuable help for you. Also, if you have any questions or doubts just let us know.