Download the gstreamer-plugins-ugly source package. Put it inside the SRPMS directory and run the rpm -i command on it to unarchive its content.
Open a text editor and edit the spec file available under SPECS. The package names vary between Moblin, Fedora and RPM Fusion and this needs to be fixed in the header. And in this example only the plugin libmad will be build so that's why many lines will be commented. In fact the only build dependencies will be libmad, libid3tag and liboil. I have put the diff on Snipt. To apply it use the patch command like patch -p0 < gstreamer-plugins-ugly.spec.diff. Don't miss the patch(1) man page to know about the -p option.
Now build binary packages with the command rpmbuild -bb SPECS/gstreamer-plugins-ugly.spec. Wait a minute and you should have a ready to install gst-plugins-ugly package within the RPMS directory.
You can more or less repeat this task for DivX and other video codecs support. For that you'll have to build the GStreamer FFmpeg plugin (gstreamer-ffmpeg source package).
Update: Regarding FFmpeg, it can be build from the RPM source package without external requirements, in fact it doesn't have any hard dependencies. Or you can even compile the gstreamer-ffmpeg plugin only with the internal FFmpeg sources since it is optionaly linked to an external FFmpeg library. In both cases the provided SPEC files have to be modified.