What about a mutual draw-down of SK and NK forces in the region into defensive postures? NK sounds like it relies on artillery as a first step in a strategy to capture Seoul, but keeping its artillery pointed at Seoul could be considered a defensive deterrent. This kind of drawdown could be coupled with the US guaranteeing it will come to SK's defense if and only if SK is attacked by the North, and China guaranteeing it will come to NK's defense if and only if NK is attacked by the South, with both China and the US declaring they will not give any assistance if there is not a clear aggressor. At the same time, get both sides to agree to stop military tests and drills in near the DMZ or on any disputed border. Keep building on SK investments into NK and let China slowly lean on NK and push it to reform (read somewhere that CHina had been doing gentle prodding towards reform in both NK and Burma).
I dunno.