Digitally sign email in ruby with S/MIME

Question

Is there a ruby way to digitally sign email messages via S/MIME? Our group uses PKI and our users are conditioned to expect digital signatures for important messages.

I know I can invoke the openssl command line tool:

openssl smime -sign -signer $CERT_FILE -passin pass:$CERT_PASS
  -in $UNSIGNED_MAIL -out $SIGNED_MAIL -certfile $CERT_CA_FILE
  -from 'your ' -to 'recipients <email@address>'
  -subject 'The Subject'

but I am hoping for a ruby solution.