It’s clear this is not ideal, but Can one take a dual band WAP or hAP and link 5 gHz NV2 and re-transmit on 2 gHz. 40 Mhz channel on 5, 20 on 2Ghz.
The range on 2Ghz so low due to congestion. 5Ghz band is open. want to also NAT, band limit and firewall on the radio,
Both radios can be used for completely different tasks, also for your scenario (one radio as access AP, the other one for upstream) with whole routing/firewalling in between.