Sirius tried not to look too disappointed. Really, he did. "Better hurry up about it, then. I'm not waiting until my next birthday for someone to be inside a cake." It couldn't be that difficult, could it? Just make a gigantic hollow cake, stick someone in it, and cut a little hole for air.
He might have to try it for Fred's birthday. Whenever that was. It didn't matter enough to bother asking right then because it was HIS birthday, and no one else's birthday could steal his thunder.
"Looks like you've gathered a good bunch, but I'll have to get back to you feedback-wise." Sirius tipped back a good swig of ale. "How can I say when I've only just arrived, mate?"