Kugelblitzes are like any other low-mass black hole: the smaller they are, the faster they evaporate. If you have a black hole large enough that it doesn't evaporate quickly, it'll likely destroy your nearby structures meant to contain it, and it'd pass right through regular matter - unless it was very charged, there'd be no way to hold it in place. If you get it small enough that it's gravitational field is sufficiently weak so as not to destroy your structure, it'll basically destroy itself in minutes to seconds, releasing energy on the level of an atomic bomb. Much of that energy will be in the form of light, which could theoretically be reflected, but there will also be tons of neutrons and other particles we couldn't just reflect back towards the black hole. Even if we could reflect all the regular stuff, including the neutrons, neutrinos released by the Hawking radiation would pass right through our meta material and the black hole would still evaporate.