I've painted numerous rims.... you just need to get a slight texture to the surface via scuffing and sanding, clean, apply a primer coat with paint or dedicated primer. I would put 2 primer coats and 3 top coats then a clear... but I'm not a pro at wet paint.
sand with 220 grit sandpaper etch primer let dry for 1 hour spray acoat of 2k high build primer let dry for 2 hours, sand with 600 grit sand paper paint & clear