Some individuals may prefer to have elbow tracking over feet tracking, either due to having pre-set lying/sitting positions or because they'd just like to test out/debug the new feature.
Presently, you're not capable of doing this, as trackers 2 and 3 always bind to the feet, regardless of location.
I've tried setting the tracker roles to disabled
AND
properly set to elbow, but it doesn't make a difference.