We maintain a list of well-known paths in bundle common paths from lib/paths.cf. It will never be exhaustive. Without support for leveraging functionality like $PATH () it would be nice to be able to extend the variables defined in lib/paths.cf without having to modify the vendored policy.
This snippet illustrates a way that users could define their own variables tagged with paths.cf. Those variables could then be pulled in to bundle common paths.
Plausibly we would need to add paths to the bundlesequence before services_autorun in order to resolve the variables from the custom policy that might have been resolved after bundle common paths was first resolved.