Since I had the blue kite line stretched across the living room to take photos of the ferry, I got out my Picavet rig for a picture, too.
It has a long history – initially developed to provide stability for the (early) camera attempts from hot air balloons, I think. Here’s a good description of it generally:
https://publiclab.org/wiki/picavet-rigging
And here’s my rig. It has a plastic base, and uses eye screws for the line to run through. Better would be some smooth action pulleys. But I gotta say – you don’t try to take photos from a kite expecting serious stability. For me at least, it just isn’t going to happen.
But there 
are other people using more sophisticated systems that can do better. I’m just happy with any photos – or even poor quality movies! – that I can take from my kites.