Add virtual network interface to limit internet traffic?

Question

The setup is as follows: I have a server with one network card in my LAN network. Now I want to limit the upload / download speed from / to the server but not the speed within the local network.

Wondershaper works perfectly fine but throttles all connections. Is it possible to create a virtual network interface, route the internet traffic through it, and throttle this interface? Will this work? Any hints how to do it or in general are appreciated.