I don't know about FortiClient specifically, it's a sorry piece of crap that's more often borken than not.
With openfortivpn, you can usually ignore whatever routes you receive and set up your own. I haven't tried the specific set up you talk about, but I don't see why it wouldn't work. However, you would most likely need to NAT on the machine running the Fortinet client.
With openfortivpn, you can usually ignore whatever routes you receive and set up your own. I haven't tried the specific set up you talk about, but I don't see why it wouldn't work. However, you would most likely need to NAT on the machine running the Fortinet client.