Don't do this at home. It looks so ugly because it's dangerous and vice-versa.
If you really want to write (and read) code like this:
id titleString = ((id ()(id, SEL, const char))objc_msgSend)((id)objc_getClass("NSString"), sel_registerName("stringWithUTF8String:"), "sup from C");
((void (*)(id, SEL, id))objc_msgSend)(window, sel_registerName("setTitle:"), titleString);
instead of this
[window setTitle:@"sup"];
then I guess it would be easier to write a Objective-C to C converter (if there isn't one already) and convert your Objective-C app into C for added coolness. I
One practical example would be tigr [1] - a cross platform window framework for making simple applications, could be compiled as one header drop-in only lib. You simply cannot make it one header without making calling ObjC runtime from C. Why it's necessary to make it work as one drop-in header? Well it's a new trend in C libraries, which allows using libraries with the least resistance possible, it's like a package manager but nicer - you only have one file! Great example of modern one header libs is probably the famous stb package [2].