Hello,
It could be possible to configure additional port forward rules on the VPS or even configure a port forward and configure a separate WireGuard or OpenVPN (or any other VPN protocol) tunnel but in that case I'd highly recommend to limit the incoming connections to specific source IP and define different (non default) listening ports. This configuration should not impact the two currently listening port: 51820 (WireGuard tunnel) and 44158 (Helium port forward). The only issue is the configuration itself would get quite extensive and slightly complicated at this point, especially the iptables part.
As an alternative, we recommend our Teltonika RMS - it will work regardless of what WAN IP address is on the RUT240 WAN interface. RMS is quite extensive and there are many different options, besides logging on to the router to configure or manage it. Please find more information on our wiki here: https://wiki.teltonika-networks.com/view/RMS
Best regards,
Tomas.