iRule uncertainty

Hi, I have a pair of F5's that load balance servers from the public and internal network.

 

 

I wish to snat the nodes return traffic (hide) to the vip that was used to access them, i.e. the internal users see a different vip to the public users.

 

 

The way I see it, I apply iRules to the VIP, but I cannot do this as it is outbound from the nodes I wish to SNAT, not inbound to them.

 

 

The only other way I can see to do this is by having forwarding turned on ??? which again I do not wish to do.

 

 

Can anyone help me out here, is what I am wanting to do possible with irules ???

 

 

Many thanks