I don't see any way of doing this easily with Digest::SHA beyond changing the source and recompiling it. Of course, if that seems a bit difficult you could always take the source of Digest::SHA::PurePerl and modify it in the ways that you need.
I have looked at that module and it just looked like it had way too much that I didn't need. Anyone see anything wrong with either one of my conversions? I fell that there really close, just some simple over looked error.