I'm playing through as Liu Bei. I dont think you HAVE to be his faction for this money trick to work. But he has the ability to annex the Han empire commanderies through Unity from the beginning which I found useful.
The key is to capture the emperor before the rank of king(I think you might have to have him for this to work) Once I became King the Han empire had 123k in gold reserves and a handful of territories. I had 40 tradable territories or so. I noticed that I could annex all of the han empire as I was making claim for emperor without using unity.
Before I annexed them however I began trading all my territory to them for Gold except my Capital commandery. I maxed out all of their Gold into my reserves then annexed all my own territory back plus theirs!
I took a hit on the first few turns in terms of taxation and recalling units helped me get a positive flow of gold back. But I was instantly granted funds for a HUGE level up to all my buildings, and commanderies across my territory.
This has helped my finances tremendously while supporting me to push the other two would be emporers out of the contest.