Hi,
AS I write this, it's 2:30 in the a.m. so hopefully it will make sense...
Have you read the aquatic cultivation tips on dodec's site? At the bottom of that page is a little chapter about flowering that I wrote, which mentions all the details that I believe play a role for U. gibba to flower.
After having read it, you might wonder if you could produce the necessary conditions in an aquarium. You can, though it may be a little tough. A small filter using an airstone and which produces a small amount of bubbles would be best to keep the surface from agitating too much. Because of the filter, the plants will also be pushed onto one side of the tank, where they should remain quietly to 'thicken' up.
A small number of livebearers shouldn't pose a problem for the plants once the plants become thick enough. For example, perhaps 3 platies would be enough in a 5 gallon tank. Make sure they're the same gender, or else you'll get more.
A longer tank would be much better for this kind of setup than a taller one, but it should be possible there too.
If this just seems like too much trouble, than you can try putting some gibba in a jar of 1/3 peat and 2/3 water. In fact, my U. gibba which flowered was kept in a jar with no peat and filled with hard tap water. But the peat helps a bit with algae.
I hope that offers you a couple of new alternatives you could try.
Good luck!
Chris F.