Add Buttons to run scripts like Git Extensions

I'm looking at switching from Git Extensions to SourceTree and one of the features I'm missing is the ability to add custom commands. In Git Extensions I can add an external script configuration to do special operations. These then show up as buttons with the name I choose.

A workaround is to use the terminal button and type in the command myself but this is just a workaround for a custom button feature.

It would be really nice if SourceTree had this feature. Seems to be great otherwise. Thanks!