I trust this thread isn't dead.
A thought on continuing the pain (pleasure), but not the bruising.
I have had naughty babies, put a flat, two strip (not round) cord (small appliance cord or extension), in her bottoms & sit on them.
Time is the key. The longer you sit, the more it hurts.
Sometimes you can't be spanking so loudly, or for so long, so that's a good continuation. Very good for corner time.
I've also had her do this as she drove over to see me.
An alternative, though not as intense. You can use the stems & vines of plastic plants. They also aren't as bulky as a cord.
Makes a great tv time treat as well, for the after glow feeling.
Hopes this helps.