Annual pass upgrade question...

[4orm]

I read that you could apply the unused portion of a PHP or PH towards an annual pass, but I didn't see if I could do this with an UPH. My husband and I are planning on possibly splitting our stay with between a dream maker package with an UPH then moving to a DVC resort on points and buying an annual pass if we could upgrade that UPH to an annual as soon as we get it. Is this possible or do they only upgrade PHPs and PHs?
Thanks so much!