As aussie_chick said, part of the cut is not to accept phone calls from the cut person. If she calls from an unrecognised number, you need to hang up as soon as you hear her voice on the other end of the line--before she finishes the first word if you can manage it that quickly. She shouldn't have the freedom to yell at you on the phone.
One thing I've found handy with bean-dipping is to ask a question, especially asking for advice. It causes people to need to think carefully on something or consider a novel situation, which very easily causes them to lose the train of thought about Samantha. "Yes, I know she's like that, that's why I've cut her out of my life. Now, I've been meaning to ask you something. My niece is looking at buying her first car, and has come to me for advice. Since you know so much more about cars than me, can you tell me ... <technical question>"
Having someone explain something they know a lot more about than you works also. What are some areas they're good at? What are some questions you can ask?
The trouble is, you've cut Samantha, not your friends. If they want to vent, you can't stop them if they don't want to be stopped. Just "mmm-hmm" and "oh" and nod and be as non-committal as possible until they're done, or excuse yourself if it looks like it'll be a long one.
