I've been using this for quite some time, and it's working quite well. It takes only a short time to build, and while it requires some futzing every now and again, does its job well.
The sawhorse outfeed table is a sawhorse topped with a couple of 2x4s. The raise the top 2x4 to the appropriate height, short 2x4s were nailed between the top and bottom. It's like a really small wall.
On top of the wall are some 1x runners that support a piece of hardboard. The hardboard just rests on the fence rail and the 1x runners. Friction keeps the hardboard in place but makes it easy to move.
It took about an hour to build 2 and attach them to sawhorses. The sawhorses are still usable as sawhorses, they're just ~10" taller than they were.
No references were consulted in creating this work. If you thought of the idea before I did, congratulations!
Puckdropper