one VIP separate pools for external and internal users

As long as there is some way to differentiate internal and external users, say by IP address, then the answer is yes. You can use a Local Traffic Policy to forward traffic to server B (pool B) if the client's IP address indicates they are an internal user, and everyone else can go to server A (pool A). (I'm assuming internal users are easier to identify by IP address.) If you need more granular controls, an iRule can do that. Can you provide some more specifications on how you are differentiating internal and external users?