Update(): How to get nModified of the MongoDB WriteResult?

If I call update() via Mongo shell, it will return the number of matching documents and the number of modified documents. If I call update() via the Meteor Mongo object, however, the method only returns the number of matching documents. How can I retrieve the number of actually affected documents, i.e. nModified?

Just saw this issue https://github.com/meteor/meteor/issues/4436 and learned that there is a undocumented option _returnObject. Unfortunately, in Meteor 1.2 it is only returning numberAffected, so it doesn’t help me much.