That's what you get for not buying a reverse hyper from WSB. J/K. Seriously, though, the only ones who seem to have comfort problems with reverse hypers are thoe who have made their own.
The WSB reverse hyper comes with an awesome pad. At least the standard version does. And I was using 180lbs of weight on it tonight, so don't think it is a weight issue.
Also, like you said, you probably aren't placing yourself correctly when performing the exercise if it is causing you pain-- it is a difficult process to find the right positioning.
I am going to put my two cents in here. It is about loyalty, andif you don't want to hear a rant then skip the shit:
If you are going to decide to add reverse hypers into your regimine, buy a fucking real one from Dave Tate. They have lifetime guarantees, are perfected from years of trial and error, and support the WSB club financially. And none of your money will be wasted. If you honestly cannot afford a standard reverse hyper (800 dollars), then go ahead and do alternative exercises or save up by not buying bullshit equipment. Other than a power rack, a bar and plates, a reverse hyper is the most importanat piece of equipment you can have. Would you rather spend 200 dollars to build something fucked up or get the real thing for 600 more? I realize there are some of you out there who have made good "knock-off" reverse hypers, but they are few and far between. I seriously doubt the "power rack attatchment" reverse hyper will be of much use. END of rant.