I am coming from GitKraken where they allow you to add/remove single lines of code to a commit. That feature would make an awesome addition to Sublime Merge.
I think I had the same question. If yes, here is the (obvious ) solution:
That is basically the answer I was looking for though a little more polish would be nice (e.g., GitKraken gives you little buttons to select lines rather than selecting the line). This is close enough though for now.