I have glued so many back together I've lost count. My solution? Finally cut down the mirror covers to be narrow turn signals only, and added old fashioned handle bar mirrors. Also, dirt bike bark busters (which do not block those old fashioned mirrors like the do the stock ones.) I have pictures somewhere...
Note the mirror mounts are available on line somewhere, don't have that info immediately available but acedantinne does, he's the one who showed'em to me. He can also source the Bark Busters which don't show up on a simple search.