Our bundled/package products feature does not pull codes from the bundled products... it only gathers the download links from those products.
You can upload a list of stored codes to the bundled product directly, one line from that list would be sent with each purchase, so you load a list that reads something like this:
...and so on, with passworda and passwordb being valid passwords to unlock the downloadable ebooks. However, I'd personally recommend just scrapping that password setup altogether. This is equivalent to handing out a lock with the key in the latch already, and isn't going to provide you a significant layer of security since a password can be shared as easily as a file.