That's not Mike's Nature trick.
Here is the actual statement from Phil Jones of Hadley:
"I’ve just completed Mike’s Nature trick of adding in the real temps to each series for the last 20 years (ie from 1981 onwards) and from 1961 for Keith’s to hide the decline."
You say "a proxy stopped working" as if that was some sort of failure. It was not. Proxies are historical analogs. You cannot use tree rings to show contemporary temperatures. The decision was made to add instrumented temperature data to the end of the plot to show what had actually happened to global temperatures. The data were clearly identified by color change and legend. The use of the trick to bring the two trends into a continuous stream was openly discussed in social media, emails and by the IPCC. So, no, it was not sleazy at all. What IS sleazy is the continued use of this demonstrable mischaracterization by AGW deniers.