A good welder could "stack" a suitably sized fabrication on top of the existing aluminum clamp. You would definitely need to weld up the split on the existing clamp, so its movement wouldn't compromise the weld, and you'll still have the risk of softening the glue that's holding the parts together.

It appears to be a pretty poor design, overall, and one the manufacturer might want to address. I'd start there, but, if that goes nowhere, talk to your local biker gang, and see who welds their Harley crank case covers. That guy will know his scheisse.

Another thought: just grind off the existing lugs, and square up the top of the clamp. Have a welder weld on another split ring on top that will allow enough room for a standard band clamp.