Hmm, I think it'd be more productive to suggest a mounting method for the current U-lock than to suggest a different lock. Hey, maybe it'll help. Mijome07 has already shown a nice picture, though I wish the detail of the exact mounting product would be offered. As for me, I'll just provide a link to
Twofish Unlimited's Bicycle Accessory Fasteners page. I haven't used any of their products, but Twofish Unlimited seems highly regarded around here, and they seem to have a variety of useful fasteners.