BTNet Dual Wan with virtual gateway

[Gazza77]

I have been trying to get a dual wan set up and working on a netgate SG-6100 but cant see how i would set up the below

Main Wan 70.x.x.195/28 next hop gateway 70.x.x.193
Second Wan 70.x.x.196/28 next hop gateway 70.x.x.193

The 70.x.x.193 is a virtual gateway on the BT cisco routers which i do not have access to.

I have set WAN1 to use the 70.x.x.195 ip and the next hop gateway to 70.x.x.193
I have set WAN2 to use the 70.x.x.196 ip but cannot use the same next hop gateway

From the lan I am able to ping the 70.x.x.193, 195, 196 ip addresses but cannot figure out how i would set up the next hop gateway for WAN2.

Does anyone know how i would setup the above?