I looked into this a while back when I had my mates one in the shop. There is nothing out there off the shelf (or rather there wasn't back then, not sure now, but highly unlikely would have thought) and as Rob says the only real alternative was to replace entirely, or fabricate something.
We didnt do it in the end as wanted to keep OEM as much as possible, so matey just made do with doing more over the shoulder checks. I rode it a few times, and personally didn't think it was so bad, at least compared to the several Jap crotch rockets I had owned (Fireblade, Gixxer etc etc etc) where ever present shoulders in the mirrors are quite normal....even my HP2 sport was like that and that had long mirror arms as well....