In a Google Groups thread, AdWords API Advisor informs developers about a new feature available to the public: IncludeZeroImpression has been taken out of beta and has now been made available to all developers and should work in all versions of the API.
AdWords API Advisor offers the following words of caution:
Please note that very large reports that include zero impression rows may fail (indicated by error code 112). If your report fails as a result of enabling this option, try breaking subsequent reports down into smaller queries/reports.
We are working to make this a more scalable solution. However, we (and several of you) felt it was important to expose this feature now despite this issue. We will notify you when scalability enhancements are released.
This feature is located in the KeywordReportJob and CustomReportJob.
Users are welcoming this addition to enhance their tools.
Forum discussion continues at Google Groups.