Form fields to show page numbers dynamically?

I need to be able to use form fields to indicate "Page X of Y". I know there's an option to do this in the document footer, but it won't work for this process because the documents are being aggregated in another system and it needs to be able to combine docs and have the page numbering change to match. If you use Acrobat's footers, combining two three-page documents gives you a six page document with page numbers 1/3, 2/3, 3/3, 1/3, 2/3, 3/3 instead of 1/6, 2/6, etc.

The question: How do I set it up so each page has a field, "PageNo", that indicates the current page number, and another field next to it, "NoPages," that contains the current number of pages in the document? These fields have to be able to update dynamically on document open as the documents are combined or split in a third party system.

The main problem I've run into: Any field with the same name as another field is functionally a copy of the original field and mirrors that field's contents. So you end up with five pages marked "Page 1 of 5." I can't give the fields unique names on each page, either, because the document combining happens outside of Acrobat and could be any combination of forms being compiled into various reports. I also don't have access to the system controlling this process, it's a black box.

I'm hoping there's some document-level script out there that can be set up to run when the merged document is opened to update the page numbers and total number of pages, but I don't know anywhere close to enough about JavaScript to come up with it on my own. I've also not run across any snippets of code floating around that handle this precise issue. If anyone can offer me any insight it would be greatly appreciated, I'm at the end of my rope with this one.