Force a push with SourceTree

I started using SourceTree a few days ago to manage Mercurial repositories with my Mac. Now I ran into the problem when pushing to my remote repository creates a new head on a new branch and I would like to force it.

However, I am not able to find any specific option in SourceTree which allows me to set the force option for a push. Is it just my inability to find it or is there no possibility to set it?

Thanks in advance Michael

In SourceTree 3 you can allow it in the advanced tab:

SourceTree is finally going to add force push: https://jira.atlassian.com/browse/SRCTREE-1156

Reason: https://answers.atlassian.com/questions/54469/how-do-i-perform-a-forced-push-push-f-from-sourcetree

Edit: It is now added in SourceTree, but you need to turn the option on in the settings.