Closed loop can often be a bodge. It will always be fighting you simply because it is relying on a slow sensor to make changes to tuning.

A simple resistor might fool it, and would be the cheapest option. Certainly best to try that first before spending any money.

If you stuck a resistor in the signal line, it would offer the ecu a lower voltage so the ecu would think the bike is lean and should add a little more fuel. Although dont forget, most engines are usually only in closed loop at part throttle and low loads/rpm's anyway.