Copy files in addition to project primary output using MSBuild project references?

I have a project that is referenced by many dependent projects, and some files in that project that must be in the binary directory of the dependent projects for the dependent projects to run.

Currently, I have several custom AfterBuild targets defined: one in the referenced project to copy the necessary files to a shared location, and then one in each of the dependent projects to reach out and copy the files from the shared location to their bin directories. This works, but it's annoying to maintain and it feels brittle and hacky.

What I would like to achieve is to get my files worked into the primary project outputs for the referenced project (i.e. alongside the .dll and .pdb), such that the files are automatically copied to the dependent projects' output directories at build time via the MSBuild ProjectReference.

Is this possible? If so, what is the mechanism by which primary outputs are discovered and to which itemgroups must I add my files? Is MSBuild "hardcoded" to look only for .dll and .pdb?

For reference, I would consider myself somewhere above an MSBuild novice, but far below an MSBuild expert. I've read Hashimi's "Inside the Microsoft Build Engine," understood it mostly, and I've been able to dig through the MS targets files a couple of times for other tasks, with moderate success. This problem is beyond me so far, though.

Also, I have reviewed this similar-looking question, but it doesn't address project references; only producing additional files with a project.

Copy files in addition to project primary output using MSBuild project references?