Re: country onChange option (client)
We had the same goals during implementation, but we were limited by the issues that you are facing. We came up with a solution that works, but we are not happy with the flow and user experience.
We eneded up capturing the Country / State Province outside of the HPM, then pass its values in the HPM on a hidden field. Whenever Country / State Province change, we reload the page and HPM.
See attached screen shot. HPM is outlined in red.