I've found that getting rid of stuff on top of stuff is really hard. A sure way to get rid of that bug is to wait until he asks to replace it (which might be a rare request unfortunately) and then give him the replacement gift while you're in his house. He'll switch out the item in front of you. Otherwise your best bet is to just keep sending him furniture you like. There's no guarantee he'll replace the one you want though. I tried for ages to get rid of something in Beau's house and he ended up chucking his music player and now it's so awkward and quiet, I might as well catch him a cricket.