"PA" or "PI" is an administrative distinction and technically has nothing to do with BGP or multi-homing. You can still announce PA blocks under your own ASN. I do that today, actually.

It's the same with IPv4, by the way. An ISP can assign you a block from their allocation, you can still announce it with your own ASN as long as it doesn't violate the issuing provider's policy, you're still a customer, etc.