The obvious way to ease out a kite is using a controlled spooling winch. The Lewmar CRW400 captive reel winch is a possible example and is used by some French kite boat enthusiasts, ArmorKite. However, I'm looking for something simpler and am trying to avoid requiring electrical equipment where possible. To that end, a simple splice seems to have potential.
I've tried about 500mm of 4mm open weave dyneema encasing some 3mm dyneema. You see in the picture a pink line which anchors the outside dyneema (grey) to my car wheel. The other end is free and the 3mm dyneema (blue) goes through it to the load.
If there is load, in the example below about 20kg, and the operator does not touch the system, it locks automatically. Easing the line out is done by pulling along the splice away from the load. The example shows it being rather jerky. But after a little more practise, it was quite easy to allow it to run smoothly and under good control.
This option is being developed in concert with a steering line release mechanism that will allow one load line and 2 steering lines to be released consistently to allow a kite (paraglider in fact) to be eased out from about 7m initial flying height to an arbitrary line length.