Suppose that I am doing a literature review on a topic, and I read paper A, which makes an interesting claim and references paper B as its source. Naturally, as paper B is then the primary source, I will look up B and possibly cite it in my own paper if it seems relevant. And suppose that it turns out that paper A says nothing else that's relevant for my topic, so I say nothing about paper A.
And this seems fine if I only discovered one citation from paper A. But if I find several useful citations in the same paper, it starts to feel like plagiarism if I just ruthlessly harvest it for citations without never citing itself.
Sometimes it's easy to work in a citation in such a case. For example, if it's a review paper I'm reading, I might be able to just write in my own paper something like:
Qwerty (2009) reviews a number of a results in this field, such as the finding that over 99% of the people who contract cancer wear shoes (Keyes 1999), that pink aliens from the sixteenth dimension dislike chocolate (Pinker 2001), ...
But often there isn't really any reasonable way to work in a citation, especially not if you wish the citation to make it clear that this is where you found useful sources from. I could include a footnote or a thanks in the acknowledgements, but I've never seen anyone do that for such a reason. Are there any rules of thumb regarding the correct etiquette in such situations?