I've been using a reverse hyper machine for ten years and I've never seen anyone that's too tall for machine. Are you sure you're doing them correctly? If in fact your legs are too long I would try to build up the height on the pad where your stomach rests. This would raise your hips up higher and allow more clearance for your legs. Good luck.
Haha....you're not familiar with the world of sub par equipment are you? Flip through a gym equipment magazine some time, and you'll see lower quality/poorly designed versions of almost every piece of powerlifting equipment.
I've seen crappy versions of the reverse hyper and other pieces of equipment. I've been powerlifting and strength training for 23 years and lifted in many gyms. It didn't occur to me that he would be using some knock off of a reverse hyper. Westside has the only real reverse hyper and it is well worth the money.