I've never heard of an end user ISP that would announce and route a customer owned block of addresses. They'll all give you a static allocation, but it will be in their block. Maybe if you were a huge customer they could do it... but I can't believe they would go to that much trouble for the measly <$100/month they get from me.

Also, I very much don't want all my outbound internet traffic to come from a permanent address range I am publicly known to own. I'd still want an ephemeral /56 for outbound traffic that changed from time to time.