Failover WAN ips with single gateway

[xkpx]

I got 4 static ip's  and single gateway is it possible to use failover/load balance for them?
Router have wan/lan ports only and it's virtualized in proxmox with added few virtual nics (attached to actuall WAN interface).
Problem is that when i create like 2/3 WAN interfaces with static ip , gateway is already used from the first one.
Can you give me some tips how ot achieve this ?
Thanks in advance