I have suggested a different approach to those listed above to dealing with the demon and that is to engage with it in the relational.
Instead you acknowledge its power in the therapy process and begin talking to it and forming relational contact when and how it wants. You don’t have a choice to do it any other way. As Berne says, it holds all the cards to play at any time it wants.
Since that time the work on this concept has continued and the demon like qualities that can also be found in the archetype of Lillith, are applicable to more people but in less pure form as described here.
The therapist needs to build a special kind of relational contract with it over a period of time, and regularly maintain that contact in the therapeutic process. One has to go along with its destructiveness at times which can require some very wily and shrewd therapeutic interventions.