Damn. This reminds me of a really good one where Fred and George are working with Hermione and totally in love with her. They invite a hooker who looks like her into the office while they think she's gone, but can't go through with it and she hears the whole thing.
I can NOT seem to find/remember it. I hope this summary, sloppy though it is, will help someone who knows it to let you know. If I find it, I'll post it for you.
Sorry. D;