[Plugin: Jetpack] Editing sharing messages (and adding bitly) on Jetpack?

I am using JetPack’s social sharing system but I do not see a place where I can edit what is being shared on social networks. For example, right now when someone clicks on Tweet This on a post they see: Post name | Long URL. That’s it. I want to make it be “Post name | Blog name | Bit.ly link” (I have my own Bit.ly which is a link shortening account).

Is this possible to set it up that way?

If so, can I customize Twitter separate from Facebook and the others? I’d love to make that one “Post name – Bit.ly link via @myusername”

I have been searching a while for a solution to my problem with no avail. Thanks for the help!!