Thank you for reaching out!
While carriers obviously do not disclose how they detect if mobile data is used by more than one user, usually it is done by inspecting the TTL (Time-to-Live) value of the outgoing packets. If the TTL value is less than 64, then the carrier assumes, that there must be other devices using the same gateway device.
TTL packets get their value decreased every hop, which in practice usually means every router. So if you have a device behind the router, the device sends out a packet with a TTL value of 65, then the router decreases it by 1, and the TTL value is now 64.
To avoid this, the IPtables rule can be used. Navigate to Network → Firewall → Custom Rules and paste this rule:
iptables -t mangle -I POSTROUTING -o wwan0 -j TTL --ttl-set 65
This command is adapted to the RUTX series of devices, running v07.02.7 of RutOS. wwan0 is the mobile interface name and may be different for other devices.
A different command could also be used for increasing the outgoing TTL value:
iptables -t mangle -I POSTROUTING -o wwan0 -j TTL --ttl-inc 1
This will increase the value by 1, but the number can be modified.
The original solution for this was provided here.
More information about TTL target in IPtables can be found here.
This solution does not guarantee, that carrier restriction will be avoided, but it's worth trying out.
Also, you might not be able to achieve the same speed as your mobile device, as the architecture of these devices varies greatly. Please refer to this article for more details.
Let me know if it helped!