Server should use the other WAN IP

[nyit_dk]

Hi

I have 2 sites wich is connected via IPSEC.
On site A there is only clients, On site B there is only 1 server.

When the server on site B connects to the internet, it is using site B's WAN address.

How do I configure my setup so that the server one site B is using the WAN on site A?

Thanks in advance.