I found creating a reverse patch between two know end-points and applying that patch would work. This presumes that you have created snapshots (tags) off of your master branch or even a back up of your master branch say master_bk_01012017.
Say the code branch you merged into master was mycodebranch.
git diff --binary master..master_bk_01012017 > ~/myrevert.patch
git apply --check myrevert.patch
git am --signoff < myrevert.patch
git branch mycodebranch_fix
git checkout mycodebranch_fix
git revert [SHA]