Remove Express Payment Gateway Options?

[gil1]

I have a Payment Gateway script which removes all payment gateway options except for one. This works on the payment step however I noticed that it does not affect "Express" checkout options such as Paypal and Amazon:

Is there a way to remove Paypal & Amazon express payment methods using Shopify Scripts editor?

Input.payment_gateways.delete_if do |payment_gateway|
    next unless payment_gateway.name != ALLOWED_GATEWAY
    puts payment_gateway.name
  end

This is the script. For now, I've resorted to just adding custom Javascript to the checkout.liquid layout but I'd very much prefer relying on the Script Editor if possible.