routing with different default gateway??

We have a LTM pair running 9.2.5. This unit handled several pool subnets with just one external vlan for the Virtual Servers. There is a default gateway configured. Due to budget constraints we just configured another vlan to connect us into a whole different additional L3 switch. The problem is that any traffic destined for Virtual Servers on the new 2nd external interface still gets routed back out the default gateway which goes to the orignal L3 switch 1. How can I make anything going to the new external interface(new switch) use a different default gateway so that it hits the new switch instead of the orignal one? Any help/examples are highly appreciated! Thank you...