You may want to try associating a route-map to the nat pool. Then match the IP addresses that you want to route outside one of the "ip nat outside" interfaces, and 'set ip default next-hop ' Do the same thing for the second nat pool you create, except route out the other interface. You can match the traffic by creating an ACL. It may look something like this:
access-list 5 permit 192.168.1.1
access-list 10 permit 192.168.2.2
ip nat pool TestPAT1 172.33.1.1 172.33.1.1 prefix-lenth 26
ip nat inside source route-map nat pool TestPAT1overload
route-map nat deny 5
match ip add 10
route-map nat permit 10
match ip add 5
set ip default next-hop
ip nat pool TestPAT2 172.33.2.2 172.33.2.2 prefix-lenth 26
ip nat inside source route-map nat2 pool TestPAT2overload
route-map nat2 deny 5
match ip add 5
route-map nat2 permit 10
match ip add 10
set ip default next-hop
This might work...Good Luck!