I also had problems with a set of 225/50x16s on my 300e. Switched to a set of Continental 205/55x16s, no problem.
However, if it is only rubbing on the one wheel well, you might want to consider having your best local body shop rework the inner lip of the fender well.
Although, it might be cheaper and more productive to just get the correct tire size. By the way, I am quite satisfied with my continental tourings and they were reasonably priced!