In the spirit of out of the box thinking...

A radically simpler and non-technical arms race approach to this is simply to apply a "leech tax".

Since we are all scored on GPS traces it would be straightforward and operationally 100% automated to simply add 5-10 seconds to each pilot's time on course for every minute they spend climbing in a thermal that another glider found before them. You get no tax if you arrive within 20 seconds of pilots in the thermal ahead of you and a thermal remains "hot" from a tax perspective until 2 minutes after all the gliders arriving in front of you have left. You can set an upper limit of 5 or 10 minutes of added time or leave it unlimited. Scoring programs could also report leeching statistics for each pilot which would be interesting to see regardless.

That would certainly cut down on visual and electronic leeching and would encourage more pilots to lead out on course, reduced time spent scouting Flarm targets.

Depends on whether leeching is the main concern.

9B