There isn't a way to set any Additional Behaviours for a git project because Multi-Branch Project Plugin depends on SCM API Plugin that is not supported specific git options.
I added more options to this plugin for a git project.
Fix #82: Add options for additional behaviours for
a git project
If you would like additional behaviors for Git, please submit changes to the Git Plugin.
thank you for your review.
I'll consider implementing this feature against Git Plugin, thanks.