Currently package installer scripts cannot access to the manifest to process it.
For components in the installer script you can get the manifest with something like:
$manifest = $parent->get('manifest');
Actually that will not work for packages. Neither:
$manifest = $parent->getParent()->manifest;
[fix] package uninstaller cannot access the manifest
[imp] use the getManifest() parent method
I'm going to close this one only because the CMS is going to take over maintenance of the Platform. Please resubmit against the CMS repo. Thanks.