Wow, I just had to try this and last night I put a butt plug in before diapering myself for bed. What an incredible feeling. After about 6 hours I had to get up and remove it then just re-taped my diaper in place.
I do have to say, this would be an excellent form of punishment that you would be sure to enjoy. A nice sound spanking, butt plugged and diapered. And, left that way for the whole night. If you got any sleep at all it would be minimal.
I also found that a full control girdle helps keep the butt plug deep in your bottom. If you body involuntarily tries to push the butt plug out, the girdle will make sure it goes right back in.