Just had this same problem on my 533i when I was doing the front rotors. I took a drill and a hardened bit and trilled the head of the bolt off until the rotor fell of and landed on my foot This left enough of the bolt that I could use channel locks to get the rest of the bolt off and replace it. I would assume that the 190e would use the same set up as my BMW. If you do try this make sure you are very careful not to drill into the hib and drill out the threads.
Why would the rotor make a clunck? The hex head bolt just hold the rotor slightly on and keeps it in place. The actual rotor is kept on by the rim and the bolts that hold the rim on. Correct me if I am wrong.