Still up in the air. When I ride our tandem, I will be with my Merrill mountain boots, or sneakers- both of which have the 17mm (almost 3/4") added to the sole of the shoe. When I ride my mountain bike which I have somewhat converted to a hybrid with smooth tires to commute daily, I use SPD A530's, which are two sided. One for cleats, the other side is flat for street shoes. I have been using the cleat side when I go out with my riding group, and when I commute. I have not had any back issues the last 6 weeks that I have been using the cleats. Those shoes are not altered. Can't figure out a way yet, but I am considering making a mold of the bottom of the shoe, then making the appropriate sole mate to slip on, and then add the appropriate shims at the cleat. As it developes, I will post. Hope this helps.
LS