Reuse DNG modules and artifacts across different projects
Accepted answer
Donald's answer is correct, as each project has set of artifacts and attributes, so that would can cause all kinds of havoc if those do not match, so between projects we don't support that.
If you have some modules and artifacts that are common for various projects, I would say to separate these in a different (master) project and associate these projects and use links to maintain their relation.
The concept of a placeholder artifact pointing to the original artifact does not exist, and would come down to a kind of implicit linking anyway.
As you are using 6.0.4 you can do that at a more granular level using components and pull them together in a GC.
On a sidenote, a set of articles were just published on configuration management and best practices, maybe these can help too: Guidance on adopting the IBM CLM configuration management across the lifecycle.