I think you're missing the point. We don't need any incentives, they're there already but many simply won't have the option to upgrade. A large percentage of FOs won't upgrade not because they're bypassing by choice but because they'll turn 65 before they'll have a chance to do so.

This is not about needing an incentive, this is about the present realities. 5 days ago I had a conversation with a guy about just that. He'll turn 65 in 7 years. Optimistically speaking he's at least 10-11 years from earliest possible left seat (any domicile/any airplane, qol not even being considered). So he'll retire as an fo which he's ok with. However, for the rest of his life his pension will be 20% less than if he'd been a captain for a single day. That's what I call the secondary B-plan and it should be changed because so many new-hires nowadays are older than in the past.