you cant route based on source ip with firewall only with router possiable by PBR

you can make to static routes each one point to deffrent router with deffrent metric

in this case it will make the topology like active standby which not good in your case

but you can use sub interfaces on your ASA intis case make each subinterface in deffrent subnet and deffrent security level

and let each subinterface use deffrent hsrp instance

or there is another way

IF you dont use VPN on your ASA u can achive it by useing multiple context

in multiple context you gonna separate your firewall virtualy

so if you have two vlans in your inside network (two deffrent subnets)

then each subnet will use deffrent firewall virtually

u goona divide the internal interface to two subinterfaces

and you can use one outside interface shred between the context or also separate it to two subinterfaces

and allocate those interface to each context

so you gonna deal with each context as deffrent firewall

and you can use deffrent HSRP instance on each context

but with multiple context you cant use VPN on the firewall

*****use the following method*****

THE OTHER WAY WHICH ALSO I SUGIST YOU TO TRY IT WHICH IS THE Transparent Firewall

in the case your firewall will operate in L2 mode

so you can use the routers HSRP IPS AS there is no firewall in the path

which i thnk helpful in you case aslo

in transperante mode the defaultgate way for your client will be the hsrp IP because the firewall will not have any IPs exept for managment

also the useres will be in the same IP subnet as the gateway in your case HSRP VIP

and also you can control the network security through the firewall normally

try this way and let me know

see the following link for configuration

http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_configuration_example09186a008089f467.shtml

please, Rate if helpful