Adding namespace to XML Digital Signature

I'm signing a SAML token with an X509 certificate, and getting what looks like a good signature except for one issue that seems relatively small, but that is causing me a huge headache. My signature looks like this:

<Signature xmlns="http://ift.tt/uq6naF">
   <SignedInfo>
      <CanonicalizationMethod Algorithm="http://ift.tt/y9fQ1c" />
      <SignatureMethod Algorithm="http://ift.tt/zf1Wx4" />
      <Reference URI="#[removed]">
         <Transforms>
            <Transform Algorithm="http://ift.tt/A1C4L2" />
         </Transforms>
         <DigestMethod Algorithm="http://ift.tt/yuvO4a" />
         <DigestValue>S4...ku4=</DigestValue>
      </Reference>
   </SignedInfo>
   <SignatureValue>oav...T7E=</SignatureValue>
   <KeyInfo>
      <X509Data>
         <X509Certificate>MII...KFl</X509Certificate>
      </X509Data>
   </KeyInfo>
</Signature>

What I need is to add a namespace, ds, so that the signature looks like this:

<ds:Signature xmlns:ds="http://ift.tt/uq6naF">
   <ds:SignedInfo>
      <ds:CanonicalizationMethod Algorithm="http://ift.tt/y9fQ1c" />
      <ds:SignatureMethod Algorithm="http://ift.tt/zf1Wx4" />
      <ds:Reference URI="#[removed]">
         <ds:Transforms>
            <ds:Transform Algorithm="http://ift.tt/A1C4L2" />
         </ds:Transforms>
         <ds:DigestMethod Algorithm="http://ift.tt/yuvO4a" />
         <ds:DigestValue>S4...ku4=</ds:DigestValue>
      </ds:Reference>
   </ds:SignedInfo>
   <ds:SignatureValue>oav...T7E=</ds:SignatureValue>
   <ds:KeyInfo>
      <ds:X509Data>
         <ds:X509Certificate>MII...KFl</ds:X509Certificate>
      </ds:X509Data>
   </ds:KeyInfo>
</ds:Signature>

It seems like this should be something I could do during while computing the signature or importing the signature block back into the existing XML document, but, for the life of me, I can't figure out how I should be doing it. I've searched online and found several people having this issue, but haven't found a good example on how to fix the problem.