Document Library is the place where binary data goes. Web Content is a specific type of content that has nothing to do with binary (or other) uploaded files.
I can't imagine any business requirement where the storage place is specified. I can imagine a presentation requirement, but that has nothing to do with the storage location of documents.
In other words: You didn't find anything because there's no way. You also wouldn't try to buy groceries in the electronics store just because somebody told you so. This is comparable.
If you let us know about the underlying business problem that you're trying to solve, we might generate ideas how to design/implement. Just make sure they're business language, not implementation details.