How do you add version comments from within the Office document when checkout is not required?

I have a library with Version-ing enabled. Check out is not enforced.

How do I add version comments from within Office (IE, Excel)?

I want to do this without having to manually check out the document via SharePoint before hand(this is my current work around).

Ideally, I'd like to be able to checkout the document from within Office.

I don't want to make checkout required for the whole library.

(edit: SharePoint 2013 and Office 2013)