Step 1: Take Hong Kong
Step 2: Take Shaozhou (the province next to Hong Kong)
Step 3: Quickly occupy some territories of China, Taiwan is a easy target, make sure step 1-3 is done in 2 months. The peace event should fire.
you need around 12 divisions to execute that, make sure you done it fast, or else, the Chinese would gather their massive army and crush your puny army. You might beat their army, but you won't be able to win totally without an enormous army of 100 divisions. (China is however, having a crappy AI that is willing to give away land after you occupy a few province of them)
This is totally realistic, had the Opium war went on for longer (all hail the cowardic empeor!), the British would be all pushed back into the sea.