Adding a commit to the front of my branch?

Normally to add commits on my branch, I perform an interactive rebase:

$ git rebase -i origin/master

I mark the commit I want to put the new commit on top of as 'edit'. However, if I want to add a commit to the front of my branch, I don't really have a commit to mark as "edit". I tried to be tricky with this, and did:

$ git rebase -i origin/master^

However this doesn't work if my merge-base is a merge commit. I get a ton of superfluous commits in my TODO file.

Is there a built-in mechanism I can use, with relative ease, to accomplish this goal? At the moment I have to run a series of a couple of commands to do this, namely mark the oldest commit on my branch as 'edit', reset it, stash it, add new commit, pop stash, commit again, etc.

Normally I'd add a new tip commit and reorder it to accomplish this, however commits on my branch already alter this code and I don't want to create unnecessary conflicts during rebase. The patch needs to be based on merge-base.

Any advice is greatly appreciated. I'm using Git for Windows 2.7.0.