Remus and Sirius using spells during sex

[artificial_ink]

 So someone had posted an earlier request for the puppies using spells they invented to help wank. I've been looking for this post for a few days but can't find it. I believe it had a link to a fic where Sirius was using Remus as a test subject for a wanking spell but the spell wouldn't let Remus get off. Anyhoo, I'm looking for that fic or just generally spells during sex as there aren't that many when I looked through the tags for them.
Thanks. I'm going to blush in a corner now.