Mark revisions as merged without really merging them

I would like to mark revisions as merged without merging them. In SVN there is the option: 

Specifically when you work in a project were you are working with a lot of branches. For instance you have 3 branches: 

- Main line 

- Branch 1

- Branch 2

You added functionality in Branch 2 and merged them into both the Main line and Branch 1. 

After you made changes in the mainline you don't want to merge the merging revisions (Branch 2 into Branch 1) into the mainline. So to prevent this from happening I want to mark those revision as merged.