I was looking for the answer to the original question. I’m refactoring my project and wanted to separate assets from UX. I had to specify relative paths. That’s is not terribly convenient because you have to search/replace the paths anytime you move files up or down the folder structure.
Since you’re saying you’re looking for an answer, here’s the current status: You need to refer to a file by the relative path from the unoproj-file it was included in. No other paths will work.
We’ve noted the feature-request, but we have not yet made any plans for such a feature.