Multiple signatures on multiple files

I currently have an XML file that we create that includes several files (such as Word, Excel, PDF...) that are stored inline with BASE64 encoding.  Each of these files can be electronically signed by multiple parties using a standard digital signature (which hashes the content of a file with some metadata like timestamps, IP addresses, etc.) generated for each party.

Clearly, I don't want to have to repeat the encoded file as an element in each Object.SignatureProperties for since the file can have multiple electronic signatures attached (each are independent of the other signatures).

Should I do this by creating an Object element that contains just the encoded file (one Object element per file), and then create multiple Signature elements (one per each electronic signature) such that is has a Reference pointing to the Object.SignatureProperties?  From the schema, it doesn't seem that this is possible since the Object element is inside the Signature element.  I see something about "detached signatures," but it's just complex enough that I'm not sure how I should be attacking this.

Thanks,
David