We are a mostly independent M/f couple (both are on CM separately as well) that has found use for a third person in a very limited way. Note that this scenario does not include any men.

My sub is very durable but occasionally needs some "incentive" in the whipping side. She is very loyal, however, and reluctant to surrender any portion of her Top to another sub. Thus, we are seeking another female whose job will be to remain "in position" next to her, ready to accept the "reward" that she (my sub) would have gotten if she falters. If she elects to give you her reward, she will be required to service you while she watches you receive it. This is a relatively vanilla position, as the reward would simply be (safe) sexual in nature (the only reason we are seeking someone from CM is that the volunteer needs to be unaffected by the fact that the woman next to her is being whipped). Because you are there only as a contingency, the likelihood of your being used is unknown (actually, it might be very low), so it isn't impossible that your role may be nothing more than decoy. If that occurs, we can arrange for suitable satisfaction for you if you so desire/require (from her).

The fact that you might dislike being used (e.g., if you are a lesbian that doesn't care for men) would be helpful, because she will know that you are sacrificing if she doesn't come through.

We are not looking for another collared submissive, but the foregoing scenario could recur from time to time.