Hi Bruno,
Just as you said, you can design custom node for your use case.
In visionworks document, we demonstrate custom nodes with function that sort an array of keypoints.
For more detail, please refer to visionworks document:
VisionWorks Toolkit Reference
VisionWorks API
Tutorials
User Custom Node Tutorial
Document is located at /usr/share/visionworks/docs on device
Or just download it at https://developer.nvidia.com/embedded/visionworks