How to get Google Pay button working with shipping options.

[lachlanh]

Thanks for a great project, we have apple pay via the PlatformPayButton working with getting updated shipping options via the onShippingContactSelected and onShippingMethodSelected. This allows the user to select a shipping address in the apple pay sheet and see an updated price when they change their shipping address.
I am trying to find how to do the same thing for google pay. The PlatformPayButton does not seem to have callbacks for this.
I have looked at using the flutter pay package for the google pay button with flutter_stripe as a backend, but I can't find any documentation their about how to wire in callbacks for the shipping.
I can see some documentation for native android google pay : https://developers.google.com/pay/api/web/guides/tutorial#price-updates but can't find anything in flutter. Any ideas about how to build this would be greatly appreciated.