Seeing as though I think this may be useful for others, I have uploaded some code and resources to Codeplex which provides this functionality. It comprises of two components:
- A site collection feature to deploy four new custom site columns for use in Content Types or document libraries where version information is to be shown in Office documents.
- A site feature which implements an event handler to populate the custom columns with version information for any document library present in the site, including the current version, when the document was last approved, who approved it, and when it was approved.
Once the custom column information is being populated by the event receiver, it can be shown in Office documents using the Quick Parts (Office 2007) or Fields (Office 2003 or 2007) features.
You can download the solution file, source code, and instructions at http://www.codeplex.com/spversionindocs.