No WAN DNS option when using USB modem

[FTC]

Hi, I am installing an RT-AX56 with Merlin and a USB 4G modem. Everything is running fine, but I find missing the DNS configuration options in the WAN tab when the USB 'WAN' is being used. I need to do this there (at the WAN level) in order for DIVERSION to keep working. If configuring DNS filter or a LAN DNS then diversion gets deactivated.

Anyone knows if there is any way to configure the WAN DNS settings for USB or what NVRAM variables can be set to achieve this effect ? .. tried setting the variables usb_wan_dns / wan0_dns / wan_dns. But it seems like not working ... maybe missing something.

Thanks in advance

 

[FTC]

Just for reference. Found a solution/bypass here : https://www.snbforums.com/threads/primary-usb-wan-dns.55298/