Load Balancing enabled with traffic directing?

[steakboy]

Im the IT Manager over a call center with 100+ computers. We have a Fortigate 60E running ver5.4.4, build 6003. We have load balancing enabled combining 2 WAN ports.  These wan ports are from 2 different internet providers to ensure VOIP calls not dropping if one goes out. The CRM we are using is web based, and is accessible on any IP address that we set (up to 5). This CRM has introduced 2 factor authentication when logging in from a different IP address than last recorded (Even when the IP address is in the white list). Having load balancing enabled, its a coin toss as to whether it will require that 2nd authentication since load balancing will just put your connection on which ever WAN port is fastest at that moment.

My question: Can we direct traffic to this specific Customer Relation Management website to a specific WAN connection while load balancing is taking effect on all other traffic? So that way it only uses one ISP to access that website, and 2 factor authentication will only be required when you actually leave the office building.

I have attempted to set up policies, but when asked to designate outgoing WAN port, it only has 1 WAN available due to the load balancing combining the 2. 

Thanks for the input!