MultiWan and routing traffic

[kart0ffelsack]

I have 4 Wan Interfaces and one LAN interface. The Network on the LAN is 192.168.0.0/16. What I now want is routing like this

192.168.0.1 -> WAN1
192.168.0.2 -> WAN2
192.168.0.3 -> WAN3
192.168.0.4 -> WAN4
192.168.0.5 -> WAN1
192.168.0.6 -> WAN2
.
.
.
to distribute the load equal over all interfaces. I can't use load balancing for this because sticky connections aren't sticky long enough and users complain that they are logged out from their favourite social network site. I suppose I could write a Script which creates 4 Aliases and puts the IPs in in them accordingly but 16k IP entries per Alias seems quite a lot so I hope there is another way to do this.