Multihomed F5 bypassing Firewall

By default the F5 initiate server side traffic based on the routes in the routing table (including local subnets).

If you would like the F5 to have the traffic from the DMZ interface routed differently, may I suggest asking your sales engineer about vCMP, or looking into setting up a seperate route domain for the DMZ interface Manual Chapter: Working with Route Domains.

vCMP is similar to creating virtual machines on F5 hardware, and route domains are similar to a single box MPLS layer 3 VPN (VRF in Cisco / Juniper terms) for layer 3 separation. Both options may take considerable time and effort to plan and implement, but if you require layer 3 or higher seperation this is where I would look first.