1. Another choice would be a mass obliviate with the suggestion they were going to wait in the common room. How do you get around 9 people in the door without the first few panicing. Wow a bunch of impatient and nosey people.
or
2. Harry and Ginny could stay ignorant a moment long for Harry to pick Ginny up to turn her so Harry can use his mouth to pleasure Ginny. While everyone still stands there in total shock. Then when they both orgasm the everyone else explodes but need a personal love shield that blocks everyone from touching them until they feel safe again.