VPN setup for Nighthawk M5 MR5200

What I have found so far:

-LTE routers generally are not set up to have VPNs because of the strict NAT provided by mobile network providers

-VPN passthrough is enabled but not configurable on the M5

Things that are configurable:

-IP passthrough, port forwarding and port filtering are possible.

-DNS settings are configurable

Does anyone see a way to input Expressvpn manual settings for a solution with L2TP,PPTP, or IPsec configuration?

Additionally, would it be an option to have a wireless router connected to the LAN port with IP passthrough, and enable a VPN service on that WIFI router?