Enable multiple currencies but only allow the default

Our end goal is to enable users to pay in GBP, EUR and USD. However, as part of a larger project of migrating to WooCommerce we’d like to simplify this for stage 1 of the migration and enable just GBP for now, adding the others later.

Is there a way to add all 3 currencies but always use the default of GBP? When all 3 are enabled we plan to use the currency switcher. As it stands, we have no currency switcher (as we only want to allow GBP).