Adding Post Preview as Tinymce button

Hi,
I searched every nook and corner of internet but I could not find a solution to add the “post preview” as a button in tinymce, along with other tinymce buttons like full screen and all. I want to do this so as to allow writers using “front end publishing system” in my site to preview their post before submitting.

So can this be done, through some hacks. I would love hear some solutions. Thanks in advance.