Story about a brother and a sister

A while ago I read a really good story about a brother and sister, and have been looking for it for a while, but haven't been able to find it. Basically, the sister does a cam show where she masturbates and stuff for her viewers, but she let slip to them that she has a trained sub/slave. The viewers then demand that she put the sub on camera next time with her, but she runs into the problem that she doesn't actually have a sub, but she needs to do something so she doesn't lose her viewers.
With nothing else to do, she talks to her brother, and eventually convinces him to go on her show and pretend to be her sub. He does, and in order to preserve his identity he wears a mask and I think is tied down, but I'm not sure about that. Anyway, the situation obviously escalates from there.
I really want to read this story again, it was very well written, so if anyone knows the story I am talking about or if you can find it, please reply.