Hide Prices but allow add to cart if not logged in

Basically we are modding the cart slightly for a customer, who doesn't want the prices to show to clients unless they are logged in to their account.

This is a simple request, however they still want to be able to add products to their cart, and eventually get to the cart where they can create their account.

We have achieved the ability to do this by moving the add to cart section of the product order form to outside of the if display_price block.

The issue we are having is that when adding the product to the cart, when the cart is updated, it adds the sub-total and total to the cart block, showing the prices.

When refreshing, the prices disappear (they are too in a if display_prices block), so the control is there.

Is this javascript that is appending the prices, and if so, how can we stop this happening.

Any advice welcome.