I would definatly recommend using a blinder with your target rifle, espescially as I works for you with a scoped rifle. If you cannot use the blinder then the next thing that I would recomend is to learn to shoot it left handed! That is far more likely to get you the results that you would want. Use the periscope/ offfset sights as a last resort. This is from the experiance of one of my coaches. He lost the sight in his right eye, so used all the gadgets to shoot right handed using the left eye. None of them really worked very well. Then he learned to shoot left handed, and withing a month was shooting as well from the left shoulder as he had from the right. He eventually regained the sight in his right eye and in the end found he could shoot as well from either shoulder.
HTH
Alan