Hi Nico
Nobody here has tried this, so I'm afraid I can't help.
Personally, I'd be very surprised if this could be made to work.
As I understand it, a package is really just a separate set of PDFs that are actually stored as attachments, but rendered one after another as if they were all part of a single document.
I very much doubt as to whether you would be able to set up a single submit button that would submit all the forms simultaneously, collate all the data from each of them into the correct form variables, etc.
I think that the package feature is more likely to be intended for the case where you have a single form, and then multiple supporting documents (such as terms and conditions, product sheets, etc) that are "attached" to the form, and are displayed immediately following it.
Please do post your findings...
Good luck...
Howard
http://www.avoka.com