Hi Primerib, I don't think it would work with what you describe. I think all of the bidets probably have to have a normal thickness on the toilet seat itself--as the spray mechanism has to hit your butt and that mechanism probably wouldn't spray high enough because of the 3 inches. All I could think of is to buy a Toilevator (an item that you put at the base of your toilet to elevate it about 3 inches. Then use your hand rails without the raised seat. Google Toilevator and you'll see a picture of it. If you have more questions, fire away.
Laurel