The remote interface has another methods like getData, but for any reason they are not available in the client jar. The worst is getJSONData does not work and Raymond Augé said to me that this method will be marked as deprecated. In the end, there is no way to retrieve expando values using web services.
The reason is ExpandoValueService_deploy.wsdd only deploys two addValue methods and getJSONData method. Probably getData and any other methods should be added to that file.