How can I set the BRISK descriptor size in OpenCV?

Question

BRISK's default size is 512 bits. How can I generate 1024-bit descriptors?

Part of my code:

...
// create the detector
cv::Ptr<cv::FeatureDetector> detector = new cv::BriskFeatureDetector(threshold, numOctaves);
// create the descriptor extractor - scale invariant and rotation invariant
cv::Ptr<cv::BriskDescriptorExtractor> descriptorExtractor = new cv::BriskDescriptorExtractor();
...
// detect keypoints
detector->detect(imgGray,keypoints);
// extract descriptor
descriptorExtractor->compute(imgGray, keypoints, descriptors);
...