Key Binds - Middle Mouse Button with Sublime Text 2

You can look at the mouse mappings by opening Packages/Default/Default (operating system).sublime-mousemap. You can then change what you want and save it in Packages/User.

I figured it out thanks to @MattDMo pointer.

I created a file in

Packages\User\Default (Windows).sublime-mousemap

inside the file I placed

[ 
    { "button": "button3", "modifiers": [], "command": "sftp_upload_file" }
]