When a packaged based drill through is set up, a report is available to any report based on the source package.
When setting up a drill through, first specify the scope to use in the package and then, a report to use as the drill through target.
The scope of the package based drill through represents the target report in the drill definition that is shown to the user, based on the items they have in the source report.

The package-based drill through is set up in Cognos Connection.