Change the nat interface based on ip sla

[arosemena]

I have 2 ISP, ISP1 provides me with /29 and ISP2 with a /28, i have 2 LANs behind 2 NATs, one goes to isp1 and the other one to isp2, they are routed with PBR to each default gateway, what i need is have one the NATed network to failover to the second isp based on ip sla icmp echo, i can't do the ip sla on the pbr because the source ip would be from the wrong isp and it would never return the packet, is there a way to change the output interface of nat based on ip sla?, this is all running on a cisco 1921 [router on a stick 4 virtual interfaces] and a 2960 switch, that's all the equipment we currently have.

any help would be greatly appreciated.

[bezcomservices]

Without fully understanding what your explaining, why not use EEM in conjunction with IPSLA to modify your PBR / NAT rules when required.

Something like this:

ip sla 100
       icmp-echo x.x.x.x
       ...
!
ip sla schedule 100 life forever start-time now
!
event manager applet ipsla100down
    event track 100 state down
    action 1.0 syslog msg "ICMP SLA FAILED - Update PBR/NAT"
    action 2.0 cli command "conf t"
    action 2.1 cli command "UPDATE YOUR CONFIGS HERE"
    ...
!    
event manager applet ipsla100up
   event track 100 state up
   action 1.0 syslog msg "ICMP SLA RECOVERED - Update PBR/NAT"
   action 2.0 cli command "conf t"
   action 2.1 cli command "UPDATE YOUR CONFIGS HERE"
   ...