First, be aware that doing this mod defeats a safety feature. Also note, the long term effects have not been seen yet. Just so you are aware, do this at your own risk. Now, on to the mod.
To eliminate the forward rev limiter when in diff lock, you need to find the red/green wire, located at pin 15 on the ECM connector, and cut it. I would cut it far enough away from the connector that if in the future you would like to reconnect it, you have enough to do that.
Snipping the Red/Green wire at ECM pin 15 keeps the diff-lock signal from reaching the PCM. The front diff grounds this wire when diff lock engages. The ECM uses this ground signal to severely limit engine power until you hold the override button down with your left thumb. Suzuki designed the bike this way as a safety feature as the machine is harder to control in diff lock.
Here is the ECM connector