It does make one wonder whether your BB width is correct. I've never personally owned a frame where the gears were so close that a shim's width threw everything out. Doesn't that mean that the gears wouldn't fit if you had the "proper" width of seat tube. Sounds like the crank spindle is too short or the frame is screwed up, which considering the source is not likely.
Just to neaten things up, I've heard of people buying the 28.6 clamp for a retrofit, though I'm no sure who would sell that.