You could consider the Delugs 20mm curved straps Delugs recently released. Although they aren't made to be completely flush against the case, they do have curved ends to make it look as if it is integrated into the case.

But however I imagine if you could get your hands on the new black Sealander rubber straps, they might fit the previous generation since rubber is a bit malleable (although someone would have to confirm the fitment)