Subdividing an existing Repository

Several Repositories I'm interested in, e.g. MINGW-PACKAGES@GITHUB, contain multiple "products." Usually, I'm only interested in one or two.
I want to have a local repo with, e.g. iodbc from MinGW-Packages as sub-moules. I don't even need to keep local content for many of the other included products. But, I need to keep synchronized with the upstream, so I don't want to destroy the meta-data that allows me to do that.

It's not certain at this point that I will ever be invited to push what I have done up the food chain. Maybe it will always be a private fork.

I've looked at Subtrees and Submodules in the ProGit book. I can see how to use an existing submodule, but not how to isolate one out of a larger body of code.

TIA

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fn:David A Cobb
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