Highlight Mokujin at the character selection screen, then select him while and hold DOWN. Release DOWN when the "Fight" screen appears. Each time your opponent lands a successful hit on Mokujin, you will hear a wooden sound.
Before starting, set the difficulty to ultra-hard and rounds to 1. When the round begins, pause and change the difficulty to easy. You will still get paid as if it was set to ultra-hard. Note: You get paid from the settings at the start of the match, so change the difficulty back to ultra-hard before the last bit of health is gone on the cpu to make suer the next match is 5,000.