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nope, not possible. i happen to have an eos and alpha mount sitting on top of each other here on my table and the bayonet diameter of the alpha mount is to large to fit inside an eos mount. even if it were possible, it ain't easy to machine a piece of aluminum or brass that thin without warping. i'd not trust an adapter that thin and the machining cost would be quite high.
you could do a mount replacement ala leitax, no aperture control though. didn't somebody here do that with a ZA 135/1.8.
Maybe you misunderstood my idea. If I have to do that I will order a CNC mechanik do a hybride mount , that fits Sony Alpha at one end and a 0.5mm shim all attached to an used canon EOS mount ( that I have many ).The cost of labor here is very affordable, so it encourages me do some conversions my self: contax N (645)--> Canon EF <-->Sigma SA.