As you have mentioned, it works only with WooCommerce AJAX. May I request implementing the custom theme Ajax same like WooCommerce AJAX feature?

When an user change the quantity in MiniCart, it should not reload the whole widget but certain section in the mini cart. There are a couple of WooCommerce hooks and upsell plugins for mini cart will not be compatible if we are unable a solution now. For instance, we are planning to implement and test Woocommerce SmartOffers Plugin for order bump and promote certain products in the mini cart widget.

I would appreciate if we can find a viable solution, as PayPal is most trusted and prominent payment gateway for the users due to the buyer and seller protection.