PyQGIS export to JSON: writeAsVectorFormat and precission

In my QGIS plugin qgis2leaf I am exporting all layers as JSON into a JSON directory. Therefore I would like to enable the user to define the precision in the GUI. The normal "save as" dialogue in QGIS has the possibility to define the precision:

Is there any possibility to use a precision in the writeAsVectorFormat? The found documentation gives me no clue:

QgsVectorFileWriter::WriterError QgsVectorFileWriter::writeAsVectorFormat   (   QgsVectorLayer *    layer,
        const QString &     fileName,
        const QString &     fileEncoding,
        const QgsCoordinateReferenceSystem *    destCRS,
        const QString &     driverName = "ESRI Shapefile",
        bool    onlySelected = false,
        QString *   errorMessage = 0,
        const QStringList &     datasourceOptions = QStringList(),
        const QStringList &     layerOptions = QStringList(),
        bool    skipAttributeCreation = false,
        QString *   newFilename = 0 
    )       [static]