henrik: It is certainly possible to do, as clamps are available in a wide variety of sizes. Tou might have to do some machinist work as they need to clamp the frame tube evenly. Bepending on how cleanly you remove the broken clamp you might need the next size up to fit onto the tube. You will also need to get the tube fairly round so that the clamp will bear evenly upon it. You might also need to enlarge and/or lenghten the slot. It should be doable, though.