Yes, this can be done. You make calls directly into the runtime itself. I'll take a look to see if I've got an example hanging about and will post it here. The "trick" is telling the runtime to re-cache the methods for the class in question. This is done when a bundle is loaded, so the esaiest way to get this effect is to load the bundle with the methods you need... after all, unless you have the code pre-compiled into some other form (other than a bundle) or wrote in-line binary instructions (not recommended and very unportable), you had to have the code compiled at some point and may as well have put it into a bundle/framework. Then you just tell the Brundle/framework loader to load the bundle in question and the methods will appear. You can also, of course, implement a category method in any file that is linked into your executable and it will be available when the program is running.
Am curious about the application of this technique, if you'd care to share.