I also read a suggestion recently about using a piece of styro to float cuttings in a working aquarium with water. Put holes in a sheet-shaped piece of styro to stick cuttings through. The way I'm picturing it in my mind, the plants would be coming up out of the top significantly, so would need to be near a window, or under a separate light instead of the light that goes on the aquarium. The circulation and added oxygen from the action of the pump would be great, and those bubbler things - an added bonus. A thicker piece would keep the cuttings more upright. It could be turned occasionally if plants are going 1-sided from leaning toward a window.
Some kind of rigged 'big plastic straws' sticking down from the holes could prevent roots from mixing up too much until they get really long. Like cutting a square from a milk or soda bottle, then rolling it into a tube. Sticking it through the hole should stop it from unrolling.
To remove plants in the spring, styro is easy to cut, or break predictably after scoring the surface. A little messy when poking the holes and breaking the cuttings out later, but an interesting, ironic twist on the usual 'dirty mess' that goes along with plants.
I don't know anything about combining this with actual fish... That wouldn't be part of the equation for me, so just to be not misunderstood I hope, none of this is known or even thought to be safe for any kinds of fish since don't have any and am not getting any if I decide to set this up for cuttings this winter.
