SpreadsheetsService and DocumentsService cannot use ServiceAccountCredential

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What steps will reproduce the problem?
1. Create service account login via ServiceAccountCredential
2. Try to instantiate SpreadsheetsService 
3. No luck :( Constructor accepts only Application name as a parameter

What is the expected output? What do you see instead?
I want to be able to run Spreadsheets service from service account user as 
described here - 
https://developers.google.com/api-client-library/dotnet/guide/aaa_oauth#service_
account But I can only create a DriveService, not a Spreadsheets service I need

What version of the product are you using? On what operating system?
2.2.0.0 under Windows 7

Please provide any additional information below.
I would really love to have this feature implemented asap. I s there any tweaks 
I can use to be able to run SpreadsheetsService with service account? Maybe 
something that is not currently released, but under development? 

Thanks.

Original issue reported on code.google.com by [email protected] on 19 Aug 2014 at 9:16