Uninstall Preservation Action

I would like to do either of these two things depending on which is
easiest/possible:

a)
Stop a folder (and it's files) installed by the SIS from being removed during uninstallation (as oppose to reinstallation - which preserves the files). The files in the SIS generated folder are created by the user.

b)
Display a warning message when uninstall is run -  indicating that
"all files the folder will be removed if they proceed with the uninstallation. Continue? Yes/No".

I've looked at RUNEMOVE option for the .pkg but it looks like
the file displayed doesn't have any associated option to cancel the installation.

Thanks for any ideas.

Paris.