best workflow for multiple signatures on high volume of invoices?

Hi, I've searched around the forums as well as the user guides and technical documents at http://www.adobe.com/devnet/acrobat/security.php , but still not sure of the best approach to take in implementing a digital signature workflow with Acrobat 9 and Reader.

We have a high volume of invoices which require approval from multiple digital signers. Below is the basic process I'm contemplating, and then below that, my concerns and a plea for help in streamlining the process. :)

*** Basic workflow ***
1) Office administrator:
- Scan paper invoice original to pdf. In Acrobat Professional 9, insert a pdf form cover sheet which contains invoice date, vendor name, total amount, etc, plus four empty signature fields.
- Reader-enable the pdf. Certify the pdf.
- Email the pdf to signer #1

2) Signer #1
- open invoice
- sign invoice
- "Save As" (apparently required?)
- email the signed, "saved as" version back to office administrator.

3) Office administrator
- email the new version (with signer #1's signature) to signer #2...

4) Repeat process for signer #3 and #4

*** Concerns/Questions***

I've tested this out but signers find the process cumbersome. If we send an email with 10 attached invoices to a signer, it's annoying to have to go through the sign/save-as shuffle for all 10 files.

Is there any way I can set things up to just Save, instead of Save As, after signing? (There seemed to be a "Sign and Save" option in Acrobat 6, from what I've gathered. One forum poster indicated as JavaScript solution, but the Adobe docs don't recommend triggering JS after a signature event, since it risks invalidating the signature.)

Alternatively... maybe we could make the process simpler by batching all ten invoices into a single pdf. The user could browse the available signature fields buried in the various cover pages through the Signature panel. However -- each signature still prompts a "Save As". :( Any way around this? Or... is there any way I can have the user click a "Sign All" button on page 1 and have that signature appear on all the various invoice cover pages on page 17, 32, etc.?

Or... Keep the invoices separate but bundle them together as a PDF Portfolio? Any thoughts on how I could streamline the signing process with a portfolio?

Thanks for reading through and for any suggestions.