I had the same thing happen to my Alfa GTV, well, sum ***!!*** kicked it off for run, arghh!!!
Anyway, tried to glue it, bond it, gave up in the end. The only thing you can do is take it to a specialist ali welder, most tyre place know one as the puddle fill alloy wheels, and get them to weld it.
Mine lasted till I did a tonne, then the wind just ripped it clean off.