I have managed to configure two IPs from different subnets on the same card. I changed /etc/network/interfaces to have:
auto eth0
iface eth0 inet static
address 172.16.4.254
netmask 255.255.255.0
network 172.16.4.0
broadcast 172.16.4.255
gateway 172.16.4.1
dns-nameservers 172.16.4.1
iface eth0 inet static
address 192.168.1.10
netmask 255.255.255.0
The problem is that the connections over the first IP started being laggy (the response time increased greatly). For instance it takes a lot of time to start loading a webpage, but it does eventually succeed. I need a console/configuration solution. No gui.