Those routers allow the LAN interface to be given up to two aliases in addition to their primary address.
So what I did was to set the primary address to a unique RFC1918 address, which was just used for management purposes when I needed to telnet to a specific router, and then to set the alias on each router to the same, shared, public address.
I then added static routes on each router to pass traffic for our public IPs back to the linux box where the bonding was done.
The WAN ports were configured with separate public addresses - a unique one for each router.
Bridge mode wasn't used - they were acting as normal routers.
I wouldn't like to say if the P660 is particularly good or bad - they were the free routers our ISP provided with the lines.