Bank of Japan policymakers gathering for a rate review this week will face the daunting task of coming up with a reason why they can hold off on expanding stimulus for now, even as slumping oil prices keep inflation further away from their 2 percent target. Less than three months ago, the BOJ justified its shock expansion of “quantitative and qualitative easing” (QQE) as aimed at preventing oil price falls, and a subsequent slowdown in price rises, from weighing on inflation expectations.