I agree with David, that such an integration would be best placed in
pdftex.def, wouldn't it? Or am we missing something?

the .def file concept has been invented precisely for hiding the interface
pecularies from the high-level interface that is used in the LaTeX source and
that is precisely what we need here, or?

i don't think however that it should got up to graphics.cfg or at least if it
does then would would need to make much more tests finding out which engine is
being used, e.g. , \ifpdf isn't necessarily be around

but otherwise ..., where is the catch, if any?