How to fake an initial merge of two unrelated branches

We are migrating from TFS VC using git-tfs. However, because of the nature of our branches (some branches were created by copying the folders, and not via branching), we could not migrate all the TFVC history. As such, our migrated branches do not share the same base.

To simplify the problem, this is our current situation:

two branches in our TFVC server, qc and release.
the same two branches in git, but as unrelated branches
if today in TFVC I want to merge from qc to release, it shows 5 changed files
However, I cannot merge from qc to release in git, as the branches are not related.

I can run git merge qc --no-commit --no-ff --allow-unrelated-histories and solve the conflicts. That works fine. However, I need to create an initial merge first that only "connects" the branches, to then do a git merge qc and see the same 5 changed files, with the same diffs.

The reason for that is that we are still running git-tfs to synchronize. The developers need to get used to git (they have been working with TFVC since always, so now they are learning it). At some moment we will stop synchronizing, to start working with the git server. That's why we need to "fake" the history between the branches, or do a big merge that does not contain this 5 files, to then do another merge to show exactly the same differences as in TFVC.

Thanks in advance!

Solution

Checkout qc. Copy the five troublesome files elsewhere. Checkout the 5 files from release, thus overwriting them in qc so they are the same in both branches. Add and commit.

Now checkout release and do the merge.

Now checkout qc again and copy the five troublesome files back into place, overwriting them with the troublesome contents. Add and commit.

Now checkout release again, and merge again, resolving as needed.