> Did you make any progress in the meantime?

No, I don't have any ideas.

> If not, could you share your current patch?

I don't have any patches.  Here is what I use now [1].  I guess it's not
enough because GHC shouldn't fail at that stage.

> I could try to investigate.

That would be great, thanks.

[1] https://lists.gnu.org/archive/html/bug-guix/2013-05/msg00068.html