Sounds like a good idea to me.

I would try to find the smallest ice cube tray possible.
and puree the frozen food and use a cake decorating pipe bag with a small nozzle.

make the nox gelatin and pour into the tray leaving 1/4 empty
let it set for a minute or two.
Then using the frosting bag inject the mixture into the center of the gelatin.

That will be less prone to leak the frozen mix into the water.
You could freeze the unused for later use.