LDAP Adapter - Credentials?

I'm writing an operation to use the LDAP Outbound Adapter to query AD.

The operation's settings include a basic Credentials selector, to allow you to use the built in Credentials function of Ensemble. This can be referenced in the operation with ..Adapter.Credentials

But when it comes to specifying the credentials in the Bind method, the documentation indicates that only a format of $lb(Username,Domain,Password) is supported. I tried ..Adapter.Credentials and $lb(..Adapter.Credentials) but the only thing that worked was setting the three variables in plain text first in the operation itself (e.g. set Username="abc", etc).

Even if I could get the reference to the adapter credentials to work - Ensemble credentials don't include a separate Domain field, only a Username and Password.

Is the adapter's credentials selector a red herring? Or can it be made to work?