The only way I know of getting 2 ip address on one interface is by cofiguring inter-vlan routing. I know the hardware configuration of you 2524 is 2 WAN, 1 Backup, I ether, 1 con, 1 aux. I think you will need another router and connect each router via serial connections.
(LAN)--->[2524]----[other router]<---(LAN)