Piwik CustomVariables.getCustomVariablesValuesFromNameId for date range

Good Day everybody,
I wonder how to use the Piwik API method CustomVariables.getCustomVariablesValuesFromNameId to get the results combined for a range, as simply setting it in the call will result in 0 rows being fetched instead of a summed-up version of what I requested. Is this behavior changeable or will I have to iterate through all the single days in the call result’s metadata?
I’m calling the API from PHP via Request::processRequest with parameters passed in dynamically (Dashboard widget)
Crossposted this to Stackoverflow also.

I think the following works:

  • first request CustomVariables.getCustomVariables for this date range
  • look for the idsubtable X in the response
  • then call CustomVariables.getCustomVariablesValuesFromNameId passing &idSubtable=X