To give a user a limited view within the portal, you simply create a user account that cannot approve requests. This way, your customer can see the data you choose without the ability to approve requests.

If you have on-premise remote gateways configured, you can also remove access to the portal entirely by limiting user access to those computers accessible via the relevant gateway. This is controlled in the admin portal under setting Logins > User Logins, EDIT or New user, tab ACCOUNT, heading Rights, field Limit to access.work.