Prior to the introduction of MYW tickets, Disney did not allow you to upgrade tickets purchased as part of a package. I think that is no longer true.
I am positive that if you can upgrade "package purchased" MYW tickets, you will be able to get the DVC price for the PAP when you do it.
My advice is to post the "Can I upgrade MYW tickets purchased as part of a package?" question on the Theme Parks Board and hope GoldenOldie answers. She is by far the most knowledgable / credible DIS poster on tickets. IMHO, you can take her answer to the bank!
I bought a one day ticket as part of a MYW package for each of the two persons in the package. When we got to WDW, we upgraded one of the tickets to a DVC AP and the other to a 4 day MYW with Park Hopping. You have to do the upgrade to the AP at Guest Services at one of the parks. You cannot do this at the resort.