I figured that since sauerkraut contains quite a lot of calcium it probably wouldn't allow for normal spherification, so I will have to go with the reverse method.
I happened to have some horseradish (sour) cream lying around that needs using up, so I decided to try reverse-spherifying that first. Hence Oysters with Green Apple Jelly, and Horseradish Cream Spheres.

Well, it turns out that reverse spherification is awkward and untidy and I made an interesting collection of horseradish cream squids and worms. But the oyster combination tasted lovely! I'm now wondering if I could use normal spherification to make green apple juice and horseradish caviar instead?
Or I could work on this reverse spherification - wider reading suggests that it is possible to do a reasonable job - thoughts:

• use low-calcium bottled water (Evian?) to make my alginate solution
• thicken the flavour mixture with xanthan gum so it doesn't just puddle on top of the alginate
• inject the flavour mixture into a spoon in the solution.
• Freeze the flavour mix into hemispheres and drop them in the solution so they hold their shape.
• Practice??

My jelly sheets were also a bit messy - possibly I didn't use enought gelatine to set them firmly enough, and don't forget to consider how you're going to get your jelly sheets out again when you choose your setting container.
Choose a shallow tray so you can more easily turn them out.
And make sure it's quite level when you leave the jelly to set :)
Of course you could also set them in half-filled ice cube trays and just warm the tray to release the slices. Easy Peasy!

Mix the lecithin grains with hot water. I've read that leaving them to soak for an hour can help. Mix the sodium alginate with very hot water - still needs blending though. Seems to settle in less than an hour.