So, uhh "Santa's Watching" doesn't work after Santa already came!
I don't believe that Santa was an effective threat in the first case. Eli is way too smart, he knew Santa wouldn't take his toys back.
What consequences work for you?
We did use the threat that if he didn't follow instructions he wouldn't be able to play his new Lego Batman tomorrow. This one worked, but I don't know how long it will work!