Wix CopyFile before uninstall and restore after uninstalltion

I am performing major upgrade and uninstalling existing product before installing new version. But I want to retain the existing config file.

As the earlier version didnt had Permanent="yes" , it removes the config file on uninstallation.

And How can I do something like this make a copy of 'app.config' as 'app.config.bak' before uninstalltion. After uninstalltion revert it back from 'app.config.bak' to 'app.config'.

<DirectoryRef Id="INSTALLDIR">
  <Component Id="BackupConfigComponent" Guid="87368AF7-4BA2-4302-891A-B163ADDB7E9C">
    <CopyFile Id="BackupConfigFile" SourceDirectory="INSTALLFOLDER" SourceName="app.config" DestinationDirectory="INSTALLFOLDER" DestinationName="app.config.bak" />
  </Component>
</DirectoryRef>

<DirectoryRef Id="INSTALLDIR">
  <Component Id="RestoreConfigComponent" Guid="87368AF7-4BA2-4302-891A-B163ADDB7E9C">
    <CopyFile Id="RestoreConfigFile" SourceDirectory="INSTALLFOLDER" SourceName="app.config.bak" DestinationDirectory="INSTALLFOLDER" DestinationName="app.config" />
  </Component>
</DirectoryRef>


<InstallExecuteSequence>
  <Custom Action="BackupConfigFile" After="InstallInitialize" />
  <RemoveExistingProducts After="InstallInitialize" />
  <Custom Action="RestoreConfigFile" After="InstallInitialize" />
</InstallExecuteSequence>

Thanks