Canonical method of merging two projects

Hi!

What is the canonical way of merging an unrelated project into another so that all of the merged project's files appear in a sub-directory of the first?

I have two projects, A with files "a.txt" and "b.txt", and B with files "a.txt" and "c.txt", each in a separate Git repoistory. I want to merge those two projects, throwing away the B repository, and achieve a file layout that has "a.txt" and "b.txt" from A, and "B/a.txt" and "B/c.txt" from B. I.e, the two files with the same name are unrelated, and all of B's file should end up in a sub-directory.

I do not want to use submodules, since I am planning on throwing B away.

When I did this, I did a regular "git merge --no-commit", and then moved the files manually. Thankfully, I only had one duplicated file name, so fixing the conflict was easy enough. I looked through the git-merge manual page, but could not find any information about this use-case.