[jhc] How to add Num instance to Foreign.C.Types.CLong?

Hello, I'm wondering how one would go about adding a Num instance to CLong? So far as I can see in lib/jhc/Foreign/C/Types.hs it's a completely opaque data type, so I've no idea how to go about adding instances. Of course, most of these type would benefit from being members of a whole slew of classes, but I can't see how to go about doing this. Any hints? -- David Roundy