How to adapt to and from an external class

I retrieve an object from an external library, later on I need to return this object back to the library. Here's an example:

var user = dao.GetUser();
var team = dao.GetTeam();
team.Add(user);

I have already tried the following:

• Adapter external -> internal
• Adapter internal -> external

It looks like this:

var user = new UserAdapter(dao.GetUser());
var team = new TeamAdapter(dao.GetTeam());
team.Add(new ExternalUserAdapter(user));

The problem was, my internal interface now had to supply a vast number of methods that I didn't need since ExternalUserAdapter implements the external interface which is far bigger than I'd like.

I have also tried the N-Way-Adapter or Class Adapter pattern, but that didn't work, since I cannot convert an external user to an internal class adapter, ie. can't convert a cat to a dog just because they are both animals.

How can I solve this issue? I would love some blog, article or book reference addressing this issue