Just fixed this with a one-liner:
1. Create a copy of _billing.html.erb and _shipping.html.erb into your
Spree app to override it.
2. Remove the label and textfield in both files and replace with
<%= bill_form.hidden_field :country_id, :value => "152" %>
Value here is hardcoded to id:152 which is Norway. You can find the other
country ids in by searching
the countries.yml file in the Spree code.