You could use something to separate the nem from the clowns but keep them in the same tank (maybe build something out of egg crate). Then you can buy another BTA. If you feed it a lot it should grow quickly. Once it's big enough you can remove the separator. Or, if you want, buy a couple of BTAs so the clowns can "spread the love".
BTAs shouldn't be expensive, unless you're looking for a special morph. Add a post on your local forum looking for a green BTA and I'm willing to bet someone will give you one, or sell it to you for cheap.