Re: How do I make some other function call the next method?

[moon (David A. Moon)]

Pass a funarg #'(lambda () (call-next-method)) to the subroutine, and
funcall it in the subroutine.  In other words, package up the action you
want to do in the lexical context where call-next-method is meaningful,
and hand the action over in the form of a callable function.

No guarantees about how efficient this is.

By the way coerce in Common Lisp is brain-damaged.  Any code that calls
coerce is questionable (it might be right, but usually isn't).

Another approach you could take is to make a telnet-stream object
have a separate tcp-stream object that it keeps in a slot, instead of
inheriting from tcp-stream.  Then you get to control all the interactions
between telnet-stream and tcp-stream explicitly, which has its good points
and its bad points.