AD integration - multiple bindings

How do I go about creating more than one binding to AD? We've configured our LTM's with the appropriate details to enable AD authentication. However the problem is that we want several user 'levels' within AD authentication:

for example, an AD group named 'f5 Admin' must be administrators, but an AD group named 'f5 Guests' must have Guest rights only.

However, through the console, we can only specify ONE AD binding, and one role in the "External Users" setting for that binding. We need to create multiple bindings.

Or am i misunderstanding the way AD is implemented on the f5?

Regards

Dean