ePMP PTP "Airtime Fairness"?

As long as the only bottleneck in my system is my speed limit at the CPE, I can run everything wide open while the AP / CPE takes care of all QoS. I do, however, have some wireless links that cannot be improved at this time. They represent a further bottleneck on part of my network. 

I'm working with Mikrotik Queuing (PCQ), which is a great tool, but I have to limit the maximum speed in order for it to function correctly. If my ePMP backhauls could handle per IP "fairness", it would allow the link speed to rise and fall while maintaining a fair sharing of the backhaul (And I wouldn't have to limit the backhaul with the Mikrotik PCQ).

I realize this would be a different mechanism, but I'd like to know if it would be possible to implement the existing airtime fairness methods on a PTP link on a per IP basis. This would allow for maximum use of a link that may have fluctuating modulation rates, or it would ensure fair use in a severe event that may significantly degrade signal strength.

Is this a reasonable possibility or are there other ways to ensure fair use of a backhaul link that also allows for fluctuating capacity?