https://groups.google.com/forum/#!topic/google-analytics-management-api/mpMWhLq6DJg%5B1-25-false%5D

Cost Data Upload Wrapper.R

postDailyCustomDataSource = function(filename = "./YandexUpload/cost.data.splits.2013_02_11.csv", 
                                     accountId=GA.profiles$accountId[52], #uploading to 52nd accountId 
                                     webPropertyId=GA.profiles$webPropertyId[52], 
                                     customDataSourceId="XXXXX", 
                                     date = '2013-02-11',
                                     access_token = MEtoken) {

# Verified this is correct URL as it works in curl
  url2 <- paste0('https://www.googleapis.com/upload/analytics/v3/management/accounts/', accountId ,
               '/webproperties/', webPropertyId, 
               '/customDataSources/', customDataSourceId,
               '/dailyUploads/', date, '/uploads?',
               'access_token=', access_token,
                 '&type=cost',                 
                 '&appendNumber=1'
                );
  
  # Returns "Error: Bad Request"
  # rawData <- postForm(url2, 
  #                     upload = fileUpload(filename = filename,
  #                                         contentType = "application/octet-stream"
  #                                         ),
  #                     .encoding = "utf-8",
  #                     style = 'POST')

   # Works, uploads file  
   syscommand <- system(paste0('curl -X POST "',url2,'" -F "upload=@',filename,';type=application/octet-stream"'), 
                        intern = TRUE)
  
  #return(rawData)
  return(syscommand)

}