The original question in this thread was whether it was really impossible, under any circumstances, to write this in C, as part of an Objective-C implementation that you fully control. It is possible in C, if you can control the ABI. It's the people who insist on a particular pre-existing ABI who are changing the question.
Anyway, I think I've said all I'm going to say here.
Anyway, I think I've said all I'm going to say here.