Dual-WAN on ASUS RT-AC68U (378.52_2) using 2 USB-modem's

[UnicornSlave]

Router - ASUS RT-AC68U
Firmware - Asuswrt-Merlin 378.52_2
ISP - Yota (both modem's)

Is it possible to configure router for Dual-WAN in Load Balancing mode using just 2 USB-modem's?
When i choose Fitst WAN option as USB, i can't have Second WAN as USB too.

Maybe I need go another way, and plug one modem into another router (Zyxel Keenetic II), then link Zyxel to ASUS in WAN? Or maybe one of LAN port's?

Or maybe I need use USB to RJ-45 adapter?

P.S. USB modem is the only ISP option in our office.

Thank's for your help!

 

[UnicornSlave]

Any solutions?)))

Maybe this functionality present in another firmware's (like Tomato, OpenWRT)? Or another hardware (like Mikrotik)?

Thank's for your help!