You can still use precommitment, but tie it to consequences rather than to Justice. Take Edward Snowden. Say that the socially-optimal outcome is to learn about the most alarming covert government programs, but not about all covert programs. So you want some Edward Snowdens to reveal some operations, but you don't want that to happen very often. The optimal behavior may be to precommit to injustice, punishing government employees who reveal secrets regardless of whether their actions were justified.