I tried ceramic balancing beads in 14.5 x 20 Michelin XL tires with poor results (up to 20 ounces per tire). The beads helped but the tires still had bounce problems. I had them spin balanced and fixed the problem. Balancing is necessary, IMHO, not because of the improved ride but because of the irregular wear that an unbalanced tire suffers. If you want long wear, a balanced tire will last longer. I put a lot of higher speed miles on mine.
As for simply plugging these big radials, I tried that once. It cost me a tire. The outer layers sealed ok but there was apparently a little leakage past the inner layer. The tread separated as air built up between the plies. An internal patch is good on a minor leak but a patch-plug should be used on a larger puncture. That's a patch with a plug attached that pulls through the prep'ed hole.
I have been looking for super singles that fit a 20" wheel, have better than a highway tread pattern (want mud tires) and are as tall as the Michelin XL's, but have not found any.