It is simple, no need to register anymore Just add the package and you are done.
BTW, that registering was needed to load "any" file anyway (loaders registered for generic routine). The original problem is that linker excludes unreferenced library modules, which includes even modules with global constructors used for registering.
However, some time ago we he introduced ".icpp" file extension which forces inclusion of object file via altered linking process. Now this is in action for image format plugins as well.